Enable Nullable

Source/FileManager/BackgroundFileSystem.cs

@@ -5,6 +5,7 @@ using System.IO;
 using System.Linq;
 using System.Threading.Tasks;
 
+#nullable enable
 namespace FileManager
 {
     /// <summary>
@@ -16,9 +17,9 @@ namespace FileManager
         public string SearchPattern { get; private set; }
         public SearchOption SearchOption { get; private set; }
 
-        private FileSystemWatcher fileSystemWatcher { get; set; }
+        private FileSystemWatcher? fileSystemWatcher { get; set; }
-        private BlockingCollection<FileSystemEventArgs> directoryChangesEvents { get; set; }
+        private BlockingCollection<FileSystemEventArgs>? directoryChangesEvents { get; set; }
-        private Task backgroundScanner { get; set; }
+        private Task? backgroundScanner { get; set; }
 
         private object fsCacheLocker { get; } = new();
         private List<LongPath> fsCache { get; } = new();
@@ -32,7 +33,7 @@ namespace FileManager
             Init();
         }
 
-        public LongPath FindFile(System.Text.RegularExpressions.Regex regex)
+        public LongPath? FindFile(System.Text.RegularExpressions.Regex regex)
         {
             lock (fsCacheLocker)
                 return fsCache.FirstOrDefault(s => regex.IsMatch(s));
@@ -105,13 +106,13 @@ namespace FileManager
 
         private void FileSystemWatcher_Changed(object sender, FileSystemEventArgs e)
         {
-            directoryChangesEvents.Add(e);
+            directoryChangesEvents?.Add(e);
         }
 
         #region Background Thread
         private void BackgroundScanner()
         {
-            while (directoryChangesEvents.TryTake(out FileSystemEventArgs change, -1))
+            while (directoryChangesEvents?.TryTake(out var change, -1) is true)
             {
                 lock (fsCacheLocker)
                     UpdateLocalCache(change);

Source/FileManager/FileUtility.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using System.Text.RegularExpressions;
@@ -7,20 +8,20 @@ using Dinah.Core;
 using Polly;
 using Polly.Retry;
 
+#nullable enable
 namespace FileManager
 {
 	public static class FileUtility
 	{
-
-
 		/// <summary>
 		/// "txt" => ".txt"
 		/// <br />".txt" => ".txt"
 		/// <br />null or whitespace => ""
 		/// </summary>
-		public static string GetStandardizedExtension(string extension)
+		[return: NotNull]
+		public static string GetStandardizedExtension(string? extension)
 			=> string.IsNullOrWhiteSpace(extension)
-			? (extension ?? "")?.Trim()
+			? string.Empty
 			: '.' + extension.Trim().Trim('.');
 
 		/// <summary>
@@ -48,18 +49,18 @@ namespace FileManager
 		/// <br/>- ensure uniqueness
 		/// <br/>- enforce max file length
 		/// </summary>
-		public static LongPath GetValidFilename(LongPath path, ReplacementCharacters replacements, string fileExtension, bool returnFirstExisting = false)
+		public static LongPath GetValidFilename(LongPath path, ReplacementCharacters replacements, string? fileExtension, bool returnFirstExisting = false)
 		{
 			ArgumentValidator.EnsureNotNull(path, nameof(path));
-			ArgumentValidator.EnsureNotNull(fileExtension, nameof(fileExtension));
+			ArgumentValidator.EnsureNotNull(replacements, nameof(replacements));
+
 			fileExtension = GetStandardizedExtension(fileExtension);
 
 			// remove invalid chars
 			path = GetSafePath(path, replacements);
 
 			// ensure uniqueness and check lengths
-			var dir = Path.GetDirectoryName(path);
+			var dir = Path.GetDirectoryName(path)?.TruncateFilename(LongPath.MaxDirectoryLength) ?? string.Empty;
-			dir = dir?.TruncateFilename(LongPath.MaxDirectoryLength) ?? string.Empty;
 
 			var fileName = Path.GetFileName(path);
 			var extIndex = fileName.LastIndexOf(fileExtension, StringComparison.OrdinalIgnoreCase);
@@ -84,6 +85,7 @@ namespace FileManager
 		public static LongPath GetSafePath(LongPath path, ReplacementCharacters replacements)
 		{
 			ArgumentValidator.EnsureNotNull(path, nameof(path));
+			ArgumentValidator.EnsureNotNull(replacements, nameof(replacements));
 
 			var pathNoPrefix = path.PathWithoutPrefix;
 
@@ -159,7 +161,7 @@ namespace FileManager
 			LongPath source,
 			LongPath destination,
 			ReplacementCharacters replacements,
-			string extension = null,
+			string? extension = null,
 			bool overwrite = false)
 		{
 			extension ??= Path.GetExtension(source);
@@ -213,6 +215,9 @@ namespace FileManager
 					SaferDelete(destination);
 
 					var dir = Path.GetDirectoryName(destination);
+					if (dir is null)
+						throw new DirectoryNotFoundException();
+
 					Serilog.Log.Logger.Debug("Attempt to create directory: {@DebugText}", new { dir });
 					Directory.CreateDirectory(dir);
 

Source/FileManager/LogArchiver.cs

@@ -8,9 +8,10 @@ using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 
+#nullable enable
 namespace FileManager
 {
-	public sealed class LogArchiver : IAsyncDisposable
+	public sealed class LogArchiver : IAsyncDisposable, IDisposable
 	{
 		public Encoding Encoding { get; set; }
 		public string FileName { get; }
@@ -39,28 +40,28 @@ namespace FileManager
 				e.Delete();
 		}
 
-		public async Task AddFileAsync(string name, JObject contents, string comment = null)
+		public async Task AddFileAsync(string name, JObject contents, string? comment = null)
 		{
 			ArgumentValidator.EnsureNotNull(contents, nameof(contents));
 			await AddFileAsync(name, Encoding.GetBytes(contents.ToString(Newtonsoft.Json.Formatting.Indented)), comment);
 		}
 
-		public async Task AddFileAsync(string name, string contents, string comment = null)
+		public async Task AddFileAsync(string name, string contents, string? comment = null)
 		{
 			ArgumentValidator.EnsureNotNull(contents, nameof(contents));
 			await AddFileAsync(name, Encoding.GetBytes(contents), comment);
 		}
 
-		public Task AddFileAsync(string name, ReadOnlyMemory<byte> contents, string comment = null)
+		public Task AddFileAsync(string name, ReadOnlyMemory<byte> contents, string? comment = null)
 		{
 			ArgumentValidator.EnsureNotNull(name, nameof(name));
 
 			name = ReplacementCharacters.Barebones.ReplaceFilenameChars(name);
-			return Task.Run(() => AddfileInternal(name, contents.Span, comment));			
+			return Task.Run(() => AddFileInternal(name, contents.Span, comment));			
 		}
 
 		private readonly object lockObj = new();
-		private void AddfileInternal(string name, ReadOnlySpan<byte> contents, string comment)
+		private void AddFileInternal(string name, ReadOnlySpan<byte> contents, string? comment)
 		{
 			lock (lockObj)
 			{
@@ -73,5 +74,7 @@ namespace FileManager
 		}
 
 		public async ValueTask DisposeAsync() => await Task.Run(archive.Dispose);
+
+		public void Dispose() => archive.Dispose();
 	}
 }

Source/FileManager/LongPath.cs

@@ -1,9 +1,11 @@
 using Newtonsoft.Json;
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Runtime.InteropServices;
 using System.Text;
 
+#nullable enable
 namespace FileManager
 {
 	public class LongPath
@@ -15,9 +17,9 @@ namespace FileManager
 		public static readonly int MaxPathLength;
 		private const int WIN_MAX_PATH = 260;
 		private const string WIN_LONG_PATH_PREFIX = @"\\?\";
-		internal static readonly bool IsWindows = System.Runtime.InteropServices.RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
+		internal static readonly bool IsWindows = RuntimeInformation.IsOSPlatform(OSPlatform.Windows);
-		internal static readonly bool IsLinux = System.Runtime.InteropServices.RuntimeInformation.IsOSPlatform(OSPlatform.Linux);
+		internal static readonly bool IsLinux = RuntimeInformation.IsOSPlatform(OSPlatform.Linux);
-		internal static readonly bool IsOSX = System.Runtime.InteropServices.RuntimeInformation.IsOSPlatform(OSPlatform.OSX);
+		internal static readonly bool IsOSX = RuntimeInformation.IsOSPlatform(OSPlatform.OSX);
 	
 		public string Path { get; }
 
@@ -60,7 +62,8 @@ namespace FileManager
 			=> IsWindows ? filename.Length
 			: Encoding.UTF8.GetByteCount(filename);
 
-		public static implicit operator LongPath(string path)
+		[return: NotNullIfNotNull(nameof(path))]
+		public static implicit operator LongPath?(string? path)
 		{
 			if (path is null) return null;
 
@@ -93,7 +96,8 @@ namespace FileManager
 			}
 		}
 
-		public static implicit operator string(LongPath path) => path?.Path;
+		[return: NotNullIfNotNull(nameof(path))]
+		public static implicit operator string?(LongPath? path) => path?.Path;
 
 		[JsonIgnore]
 		public string ShortPathName
@@ -127,8 +131,6 @@ namespace FileManager
 				//for newly-created entries in ther file system. Existing entries made while
 				//8dot3 names were disabled will not be reachable by short paths.
 
-				if (Path is null) return null;
-
 				StringBuilder shortPathBuffer = new(MaxPathLength);
 				GetShortPathName(Path, shortPathBuffer, MaxPathLength);
 				return shortPathBuffer.ToString();
@@ -141,7 +143,6 @@ namespace FileManager
 			get
 			{
 				if (!IsWindows) return Path;
-				if (Path is null) return null;
 
 				StringBuilder longPathBuffer = new(MaxPathLength);
 				GetLongPathName(Path, longPathBuffer, MaxPathLength);
@@ -156,7 +157,8 @@ namespace FileManager
 			{
 				if (!IsWindows) return Path;
 				return
-					Path?.StartsWith(WIN_LONG_PATH_PREFIX) == true ? Path.Remove(0, WIN_LONG_PATH_PREFIX.Length)
+					Path.StartsWith(WIN_LONG_PATH_PREFIX)
+					? Path.Remove(0, WIN_LONG_PATH_PREFIX.Length)
 					: Path;
 			}
 		}
@@ -164,9 +166,9 @@ namespace FileManager
 		public override string ToString() => Path;
 
 		public override int GetHashCode() => Path.GetHashCode();
-		public override bool Equals(object obj) => obj is LongPath other && Path == other.Path;
+		public override bool Equals(object? obj) => obj is LongPath other && Path == other.Path;
-		public static bool operator ==(LongPath path1, LongPath path2) => path1.Equals(path2);
+		public static bool operator ==(LongPath? path1, LongPath? path2) => path1?.Equals(path2) is true;
-		public static bool operator !=(LongPath path1, LongPath path2) => !path1.Equals(path2);
+		public static bool operator !=(LongPath? path1, LongPath? path2) => path1 is null || path2 is null || !path1.Equals(path2);
 
 
 		[DllImport("kernel32.dll", CharSet = CharSet.Unicode)]

Source/FileManager/NamingTemplate/ConditionalTagCollection[TClass].cs

@@ -1,7 +1,9 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq.Expressions;
 using System.Text.RegularExpressions;
 
+#nullable enable
 namespace FileManager.NamingTemplate;
 
 internal interface IClosingPropertyTag : IPropertyTag
@@ -17,7 +19,7 @@ internal interface IClosingPropertyTag : IPropertyTag
 	/// <param name="exactName">The <paramref name="templateString"/> substring that was matched.</param>
 	/// <param name="propertyTag">The registered <see cref="IPropertyTag"/></param>
 	/// <returns>True if the <paramref name="templateString"/> starts with this tag.</returns>
-	bool StartsWithClosing(string templateString, out string exactName, out IClosingPropertyTag propertyTag);
+	bool StartsWithClosing(string templateString, [NotNullWhen(true)] out string? exactName, [NotNullWhen(true)] out IClosingPropertyTag? propertyTag);
 }
 
 public class ConditionalTagCollection<TClass> : TagCollection
@@ -37,6 +39,7 @@ public class ConditionalTagCollection<TClass> : TagCollection
 	
 	private class ConditionalTag : TagBase, IClosingPropertyTag
 	{
+		public override Regex NameMatcher { get; }
 		public Regex NameCloseMatcher { get; }
 
 		public ConditionalTag(ITemplateTag templateTag, RegexOptions options, Expression conditionExpression)
@@ -46,7 +49,7 @@ public class ConditionalTagCollection<TClass> : TagCollection
 			NameCloseMatcher = new Regex($"^<-{templateTag.TagName}>", options);
 		}
 
-		public bool StartsWithClosing(string templateString, out string exactName, out IClosingPropertyTag propertyTag)
+		public bool StartsWithClosing(string templateString, [NotNullWhen(true)] out string? exactName, [NotNullWhen(true)] out IClosingPropertyTag? propertyTag)
 		{
 			var match = NameCloseMatcher.Match(templateString);
 			if (match.Success)

Source/FileManager/NamingTemplate/NamingTemplate.cs

@@ -1,19 +1,21 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Linq.Expressions;
 
+#nullable enable
 namespace FileManager.NamingTemplate;
 
 public class NamingTemplate
 {
-	public string TemplateText { get; private set; }
+	public string TemplateText { get; private set; } = string.Empty;
 	public IEnumerable<ITemplateTag> TagsInUse => _tagsInUse;
 	public IEnumerable<ITemplateTag> TagsRegistered => TagCollections.SelectMany(t => t).DistinctBy(t => t.TagName);
 	public IEnumerable<string> Warnings => errors.Concat(warnings);
 	public IEnumerable<string> Errors => errors;
 
-	private Delegate templateToString;
+	private Delegate? templateToString;
 	private readonly List<string> warnings = new();
 	private readonly List<string> errors = new();
 	private readonly IEnumerable<TagCollection> TagCollections;
@@ -30,6 +32,9 @@ public class NamingTemplate
 	/// <param name="propertyClasses">Instances of the TClass used in <see cref="PropertyTagCollection{TClass}"/> and <see cref="ConditionalTagCollection{TClass}"/></param>
 	public TemplatePart Evaluate(params object[] propertyClasses)
 	{
+		if (templateToString is null)
+			throw new InvalidOperationException();
+
 		// Match propertyClasses to the arguments required by templateToString.DynamicInvoke(). 
 		// First parameter is "this", so ignore it.
 		var delegateArgTypes = templateToString.Method.GetParameters().Skip(1);
@@ -39,7 +44,7 @@ public class NamingTemplate
 		if (args.Length != delegateArgTypes.Count())
 			throw new ArgumentException($"This instance of {nameof(NamingTemplate)} requires the following arguments: {string.Join(", ", delegateArgTypes.Select(t => t.Name).Distinct())}");
 
-		return ((TemplatePart)templateToString.DynamicInvoke(args)).FirstPart;
+		return (templateToString.DynamicInvoke(args) as TemplatePart)!.FirstPart;
 	}
 
 	/// <summary>Parse a template string to a <see cref="NamingTemplate"/></summary>
@@ -69,7 +74,7 @@ public class NamingTemplate
 	}
 
 	/// <summary>Builds an <see cref="Expression"/> tree that will evaluate to a <see cref="TemplatePart"/></summary>
-	private static Expression GetExpressionTree(BinaryNode node)
+	private static Expression GetExpressionTree(BinaryNode? node)
 	{
 		if (node is null) return TemplatePart.Blank;
 		else if (node.IsValue) return node.Expression;
@@ -81,10 +86,10 @@ public class NamingTemplate
 	}
 
 	/// <summary>Parse a template string into a <see cref="BinaryNode"/> tree</summary>
-	private BinaryNode IntermediateParse(string templateString)
+	private BinaryNode IntermediateParse(string? templateString)
 	{
 		if (templateString is null)
-			throw new NullReferenceException(ERROR_NULL_IS_INVALID);
+			throw new ArgumentException(ERROR_NULL_IS_INVALID);
 		else if (string.IsNullOrEmpty(templateString))
 			warnings.Add(WARNING_EMPTY);
 		else if (string.IsNullOrWhiteSpace(templateString))
@@ -93,12 +98,12 @@ public class NamingTemplate
 		TemplateText = templateString;
 
 		BinaryNode topNode = BinaryNode.CreateRoot();
-		BinaryNode currentNode = topNode;
+		BinaryNode? currentNode = topNode;
 		List<char> literalChars = new();
 
 		while (templateString.Length > 0)
 		{
-			if (StartsWith(templateString, out string exactPropertyName, out var propertyTag, out var valueExpression))
+			if (StartsWith(templateString, out var exactPropertyName, out var propertyTag, out var valueExpression))
 			{
 				checkAndAddLiterals();
 
@@ -116,7 +121,7 @@ public class NamingTemplate
 			{
 				checkAndAddLiterals();
 
-				BinaryNode lastParenth = currentNode;
+				BinaryNode? lastParenth = currentNode;
 
 				while (lastParenth?.IsConditional is false)
 					lastParenth = lastParenth.Parent;
@@ -168,7 +173,7 @@ public class NamingTemplate
 		}
 	}
 
-	private bool StartsWith(string template, out string exactName, out IPropertyTag propertyTag, out Expression valueExpression)
+	private bool StartsWith(string template, [NotNullWhen(true)] out string? exactName, [NotNullWhen(true)] out IPropertyTag? propertyTag, [NotNullWhen(true)] out Expression? valueExpression)
 	{
 		foreach (var pc in TagCollections)
 		{
@@ -182,7 +187,7 @@ public class NamingTemplate
 		return false;
 	}
 
-	private bool StartsWithClosing(string template, out string exactName, out IClosingPropertyTag closingPropertyTag)
+	private bool StartsWithClosing(string template, [NotNullWhen(true)] out string? exactName, [NotNullWhen(true)] out IClosingPropertyTag? closingPropertyTag)
 	{
 		foreach (var pc in TagCollections)
 		{
@@ -198,36 +203,36 @@ public class NamingTemplate
 	private class BinaryNode
 	{
 		public string Name { get; }
-		public BinaryNode Parent { get; private set; }
+		public BinaryNode? Parent { get; private set; }
-		public BinaryNode RightChild { get; private set; }
+		public BinaryNode? RightChild { get; private set; }
-		public BinaryNode LeftChild { get; private set; }
+		public BinaryNode? LeftChild { get; private set; }
-		public Expression Expression { get; private init; }
+		public Expression Expression { get; }
 		public bool IsConditional { get; private init; } = false;
 		public bool IsValue { get; private init; } = false;
 
-		public static BinaryNode CreateRoot() => new("Root");
+		public static BinaryNode CreateRoot() => new("Root", Expression.Empty());
 
-		public static BinaryNode CreateValue(string literal) => new("Literal")
+		public static BinaryNode CreateValue(string literal)
+			=> new("Literal", TemplatePart.CreateLiteral(literal))
 			{
-			IsValue = true,
+				IsValue = true
-			Expression = TemplatePart.CreateLiteral(literal)
 			};
 
-		public static BinaryNode CreateValue(ITemplateTag templateTag, Expression property) => new(templateTag.TagName)
+		public static BinaryNode CreateValue(ITemplateTag templateTag, Expression property)
+			=> new(templateTag.TagName, TemplatePart.CreateProperty(templateTag, property))
 			{
-			IsValue = true,
+				IsValue = true
-			Expression = TemplatePart.CreateProperty(templateTag, property)
 			};
 
-		public static BinaryNode CreateConditional(ITemplateTag templateTag, Expression property) => new(templateTag.TagName)
+		public static BinaryNode CreateConditional(ITemplateTag templateTag, Expression property)
+			=> new(templateTag.TagName, property)
 			{
-			IsConditional = true,
+				IsConditional = true
-			Expression = property
 			};
 
 		private static BinaryNode CreateConcatenation(BinaryNode left, BinaryNode right)
 		{
-			var newNode = new BinaryNode("Concatenation")
+			var newNode = new BinaryNode("Concatenation", Expression.Empty())
 			{
 				LeftChild = left,
 				RightChild = right
@@ -237,7 +242,12 @@ public class NamingTemplate
 			return newNode;
 		}
 
-		private BinaryNode(string name) => Name = name;
+		private BinaryNode(string name, Expression expression)
+		{
+			Name = name;
+			Expression = expression;
+		}
+
 		public override string ToString() => Name;
 
 		public BinaryNode AddNewNode(BinaryNode newNode)

Source/FileManager/NamingTemplate/PropertyTagCollection[TClass].cs

@@ -5,6 +5,7 @@ using System.Linq;
 using System.Linq.Expressions;
 using System.Text.RegularExpressions;
 
+#nullable enable
 namespace FileManager.NamingTemplate;
 
 public delegate string PropertyFormatter<T>(ITemplateTag templateTag, T value, string formatString);
@@ -37,7 +38,7 @@ public class PropertyTagCollection<TClass> : TagCollection
 	/// <param name="formatter">Optional formatting function that accepts the <typeparamref name="TProperty"/> property
 	/// and a formatting string and returnes the value the formatted string. If <see cref="null"/>, use the default
 	/// <typeparamref name="TProperty"/> formatter if present, or <see cref="object.ToString"/></param>
-	public void Add<TProperty>(ITemplateTag templateTag, Func<TClass, TProperty?> propertyGetter, PropertyFormatter<TProperty> formatter = null)
+	public void Add<TProperty>(ITemplateTag templateTag, Func<TClass, TProperty?> propertyGetter, PropertyFormatter<TProperty>? formatter = null)
 		where TProperty : struct
 		=> RegisterWithFormatter(templateTag, propertyGetter, formatter);
 
@@ -59,7 +60,7 @@ public class PropertyTagCollection<TClass> : TagCollection
 	/// <param name="formatter">Optional formatting function that accepts the <typeparamref name="TProperty"/> property
 	/// and a formatting string and returnes the value formatted to string. If <see cref="null"/>, use the default
 	/// <typeparamref name="TProperty"/> formatter if present, or <see cref="object.ToString"/></param>
-	public void Add<TProperty>(ITemplateTag templateTag, Func<TClass, TProperty> propertyGetter, PropertyFormatter<TProperty> formatter = null)
+	public void Add<TProperty>(ITemplateTag templateTag, Func<TClass, TProperty> propertyGetter, PropertyFormatter<TProperty>? formatter = null)
 		=> RegisterWithFormatter(templateTag, propertyGetter, formatter);
 
 	/// <summary>
@@ -72,14 +73,15 @@ public class PropertyTagCollection<TClass> : TagCollection
 		=> RegisterWithToString(templateTag, propertyGetter, toString);
 
 	private void RegisterWithFormatter<TProperty, TPropertyValue>
-		(ITemplateTag templateTag, Func<TClass, TProperty> propertyGetter, PropertyFormatter<TPropertyValue> formatter)
+		(ITemplateTag templateTag, Func<TClass, TProperty> propertyGetter, PropertyFormatter<TPropertyValue>? formatter)
 	{
 		ArgumentValidator.EnsureNotNull(templateTag, nameof(templateTag));
 		ArgumentValidator.EnsureNotNull(propertyGetter, nameof(propertyGetter));
 
 		var expr = Expression.Call(Expression.Constant(propertyGetter.Target), propertyGetter.Method, Parameter);
+		formatter ??= GetDefaultFormatter<TPropertyValue>();
 
-		if ((formatter ??= GetDefaultFormatter<TPropertyValue>()) is null)
+		if (formatter is null)
 			AddPropertyTag(new PropertyTag<TPropertyValue>(templateTag, Options, expr, ToStringFunc));
 		else
 			AddPropertyTag(new PropertyTag<TPropertyValue>(templateTag, Options, expr, formatter));
@@ -97,7 +99,7 @@ public class PropertyTagCollection<TClass> : TagCollection
 
 	private static string ToStringFunc<T>(T propertyValue) => propertyValue?.ToString() ?? "";
 
-	private PropertyFormatter<T> GetDefaultFormatter<T>()
+	private PropertyFormatter<T>? GetDefaultFormatter<T>()
 	{
 		try
 		{
@@ -109,6 +111,7 @@ public class PropertyTagCollection<TClass> : TagCollection
 
 	private class PropertyTag<TPropertyValue> : TagBase
 	{
+		public override Regex NameMatcher { get; }
 		private Func<Expression, string, Expression> CreateToStringExpression { get; }
 
 		public PropertyTag(ITemplateTag templateTag, RegexOptions options, Expression propertyGetter, PropertyFormatter<TPropertyValue> formatter)

Source/FileManager/NamingTemplate/TagBase.cs

@@ -1,7 +1,9 @@
 using System;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq.Expressions;
 using System.Text.RegularExpressions;
 
+#nullable enable
 namespace FileManager.NamingTemplate;
 
 internal interface IPropertyTag
@@ -22,13 +24,13 @@ internal interface IPropertyTag
 	/// <param name="exactName">The <paramref name="templateString"/> substring that was matched.</param>
 	/// <param name="propertyValue">The <see cref="Expression"/> that returns the property's value</param>
 	/// <returns>True if the <paramref name="templateString"/> starts with this tag.</returns>
-	bool StartsWith(string templateString, out string exactName, out Expression propertyValue);
+	bool StartsWith(string templateString, [NotNullWhen(true)] out string? exactName, [NotNullWhen(true)] out Expression? propertyValue);
 }
 
 internal abstract class TagBase : IPropertyTag
 {
 	public ITemplateTag TemplateTag { get; }
-	public Regex NameMatcher { get; protected init; }
+	public abstract Regex NameMatcher { get; }
 	public Type ReturnType => ValueExpression.Type;
 	protected Expression ValueExpression { get; }
 
@@ -43,7 +45,7 @@ internal abstract class TagBase : IPropertyTag
 	/// <param name="formatter">The optional format string in the match inside the square brackets</param>
 	protected abstract Expression GetTagExpression(string exactName, string formatter);
 
-	public bool StartsWith(string templateString, out string exactName, out Expression propertyValue)
+	public bool StartsWith(string templateString, [NotNullWhen(true)] out string? exactName, [NotNullWhen(true)] out Expression? propertyValue)
 	{
 		var match = NameMatcher.Match(templateString);
 		if (match.Success)

Source/FileManager/NamingTemplate/TagCollection.cs

@@ -1,10 +1,12 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 using System.Linq.Expressions;
 using System.Text.RegularExpressions;
 
+#nullable enable
 namespace FileManager.NamingTemplate;
 
 /// <summary>A collection of <see cref="IPropertyTag"/>s registered to a single <see cref="Type"/>.</summary>
@@ -32,7 +34,7 @@ public abstract class TagCollection : IEnumerable<ITemplateTag>
 	/// <param name="exactName">The <paramref name="templateString"/> substring that was matched.</param>
 	/// <param name="propertyValue">The <see cref="Expression"/> that returns the <paramref name="propertyTag"/>'s value</param>
 	/// <returns>True if the <paramref name="templateString"/> starts with a tag registered in this class.</returns>
-	internal bool StartsWith(string templateString, out string exactName, out IPropertyTag propertyTag, out Expression propertyValue)
+	internal bool StartsWith(string templateString, [NotNullWhen(true)] out string? exactName, [NotNullWhen(true)] out IPropertyTag? propertyTag, [NotNullWhen(true)] out Expression? propertyValue)
 	{
 		foreach (var p in PropertyTags)
 		{
@@ -57,7 +59,7 @@ public abstract class TagCollection : IEnumerable<ITemplateTag>
 	/// <param name="exactName">The <paramref name="templateString"/> substring that was matched.</param>
 	/// <param name="closingPropertyTag">The registered <see cref="IClosingPropertyTag"/></param>
 	/// <returns>True if the <paramref name="templateString"/> starts with this tag.</returns>
-	internal bool StartsWithClosing(string templateString, out string exactName, out IClosingPropertyTag closingPropertyTag)
+	internal bool StartsWithClosing(string templateString, [NotNullWhen(true)] out string? exactName, [NotNullWhen(true)] out IClosingPropertyTag? closingPropertyTag)
 	{
 		foreach (var  cg in PropertyTags.OfType<IClosingPropertyTag>())
 		{

Source/FileManager/NamingTemplate/TemplatePart.cs

@@ -4,6 +4,7 @@ using System.Collections.Generic;
 using System.Linq.Expressions;
 using System.Reflection;
 
+#nullable enable
 namespace FileManager.NamingTemplate;
 
 /// <summary>Represents one part of an evaluated <see cref="NamingTemplate"/>.</summary>
@@ -15,13 +16,13 @@ public class TemplatePart : IEnumerable<TemplatePart>
 
 	/// <summary> The <see cref="IPropertyTag"/>'s <see cref="ITemplateTag"/> if <see cref="TemplatePart"/> is
 	/// a registered property, otherwise <see cref="null"/> for string literals. </summary>
-	public ITemplateTag TemplateTag { get; }
+	public ITemplateTag? TemplateTag { get; }
 
 	/// <summary>The evaluated string.</summary>
 	public string Value { get; }
 
-	private TemplatePart previous;
+	private TemplatePart? previous;
-	private TemplatePart next;
+	private TemplatePart? next;
 	private TemplatePart(string name, string value)
 	{
 		TagName = name;
@@ -53,14 +54,33 @@ public class TemplatePart : IEnumerable<TemplatePart>
 	private static Expression CreateExpression(string name, Expression value)
 		=> Expression.New(constructorInfo, Expression.Constant(name), value);
 
-	private static readonly ConstructorInfo constructorInfo
+	private static readonly ConstructorInfo constructorInfo;
-		= typeof(TemplatePart).GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance, new Type[] { typeof(string), typeof(string) });
+	private static readonly ConstructorInfo tagTemplateConstructorInfo;
+	private static readonly MethodInfo addMethodInfo;
+	static TemplatePart()
+	{
+		var type = typeof(TemplatePart);
 
-	private static readonly ConstructorInfo tagTemplateConstructorInfo
+		if (type.GetConstructor(
-		= typeof(TemplatePart).GetConstructor(BindingFlags.NonPublic | BindingFlags.Instance, new Type[] { typeof(ITemplateTag), typeof(string)	});
+			BindingFlags.NonPublic | BindingFlags.Instance,
+			new Type[] { typeof(string), typeof(string) }) is not ConstructorInfo c1)
+			throw new MissingMethodException(nameof(TemplatePart));
 
-	private static readonly MethodInfo addMethodInfo
+		if (type.GetConstructor(
-		= typeof(TemplatePart).GetMethod(nameof(Concatenate), BindingFlags.NonPublic | BindingFlags.Static, new Type[] { typeof(TemplatePart), typeof(TemplatePart) });
+			BindingFlags.NonPublic | BindingFlags.Instance,
+			new Type[] { typeof(ITemplateTag), typeof(string) }) is not ConstructorInfo c2)
+			throw new MissingMethodException(nameof(TemplatePart));
+
+		if (type.GetMethod(
+			nameof(Concatenate),
+			BindingFlags.NonPublic | BindingFlags.Static,
+			new Type[] { typeof(TemplatePart), typeof(TemplatePart) }) is not MethodInfo m1)
+			throw new MissingMethodException(nameof(Concatenate));
+
+		constructorInfo = c1;
+		tagTemplateConstructorInfo = c2;
+		addMethodInfo = m1;
+	}
 
 	public IEnumerator<TemplatePart> GetEnumerator()
 	{

Source/FileManager/PersistentDictionary.cs

@@ -1,10 +1,12 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;
 
+#nullable enable
 namespace FileManager
 {
     public class PersistentDictionary
@@ -13,19 +15,19 @@ namespace FileManager
         public bool IsReadOnly { get; }
 
         // optimize for strings. expectation is most settings will be strings and a rare exception will be something else
-        private Dictionary<string, string> stringCache { get; } = new Dictionary<string, string>();
+        private Dictionary<string, string?> stringCache { get; } = new();
-        private Dictionary<string, object> objectCache { get; } = new Dictionary<string, object>();
+        private Dictionary<string, object?> objectCache { get; } = new();
 
         public PersistentDictionary(string filepath, bool isReadOnly = false)
         {
             Filepath = filepath;
             IsReadOnly = isReadOnly;
 
-            if (File.Exists(Filepath))
+            if (File.Exists(Filepath) || Path.GetDirectoryName(Filepath) is not string dirName)
                 return;
 
             // will create any missing directories, incl subdirectories. if all already exist: no action
-            Directory.CreateDirectory(Path.GetDirectoryName(filepath));
+            Directory.CreateDirectory(dirName);
 
             if (IsReadOnly)
                 return;
@@ -33,13 +35,14 @@ namespace FileManager
             createNewFile();
         }
 
-        public string GetString(string propertyName, string defaultValue = null)
+		[return: NotNullIfNotNull(nameof(defaultValue))]
+		public string? GetString(string propertyName, string? defaultValue = null)
         {
             if (!stringCache.ContainsKey(propertyName))
             {
                 var jObject = readFile();
                 if (jObject.ContainsKey(propertyName))
-                    stringCache[propertyName] = jObject[propertyName].Value<string>();
+                    stringCache[propertyName] = jObject[propertyName]?.Value<string>();
                 else
                     stringCache[propertyName] = defaultValue;
             }
@@ -47,7 +50,8 @@ namespace FileManager
             return stringCache[propertyName];
         }
 
-        public T GetNonString<T>(string propertyName, T defaultValue = default)
+        [return: NotNullIfNotNull(nameof(defaultValue))]
+        public T? GetNonString<T>(string propertyName, T? defaultValue = default)
         {
             var obj = GetObject(propertyName);
 
@@ -72,21 +76,21 @@ namespace FileManager
             throw new InvalidCastException($"{obj.GetType()} is not convertible to {typeof(T)}");
         }
 
-        public object GetObject(string propertyName)
+        public object? GetObject(string propertyName)
         {
             if (!objectCache.ContainsKey(propertyName))
             {
                 var jObject = readFile();
                 if (!jObject.ContainsKey(propertyName))
                     return null;
-                objectCache[propertyName] = jObject[propertyName].Value<object>();
+                objectCache[propertyName] = jObject[propertyName]?.Value<object>();
             }
 
             return objectCache[propertyName];
         }
 
-        public string GetStringFromJsonPath(string jsonPath, string propertyName) => GetStringFromJsonPath($"{jsonPath}.{propertyName}");
+        public string? GetStringFromJsonPath(string jsonPath, string propertyName) => GetStringFromJsonPath($"{jsonPath}.{propertyName}");
-        public string GetStringFromJsonPath(string jsonPath)
+        public string? GetStringFromJsonPath(string jsonPath)
         {
             if (!stringCache.ContainsKey(jsonPath))
             {
@@ -96,7 +100,7 @@ namespace FileManager
                     var token = jObject.SelectToken(jsonPath);
                     if (token is null)
                         return null;
-                    stringCache[jsonPath] = (string)token;
+                    stringCache[jsonPath] = token.Value<string>();
                 }
                 catch
                 {
@@ -110,7 +114,7 @@ namespace FileManager
         public bool Exists(string propertyName) => readFile().ContainsKey(propertyName);
 
         private object locker { get; } = new object();
-        public void SetString(string propertyName, string newValue)
+        public void SetString(string propertyName, string? newValue)
         {
             // only do this check in string cache, NOT object cache
             if (stringCache.ContainsKey(propertyName) && stringCache[propertyName] == newValue)
@@ -122,7 +126,7 @@ namespace FileManager
             writeFile(propertyName, newValue);
         }
 
-        public void SetNonString(string propertyName, object newValue)
+        public void SetNonString(string propertyName, object? newValue)
         {
             // set cache
             objectCache[propertyName] = newValue;
@@ -160,7 +164,7 @@ namespace FileManager
 			return success;
 		}
 
-        private void writeFile(string propertyName, JToken newValue)
+        private void writeFile(string propertyName, JToken? newValue)
         {
             if (IsReadOnly)
                 return;
@@ -190,7 +194,7 @@ namespace FileManager
 
         /// <summary>WILL ONLY set if already present. WILL NOT create new</summary>
         /// <returns>Value was changed</returns>
-        public bool SetWithJsonPath(string jsonPath, string propertyName, string newValue, bool suppressLogging = false)
+        public bool SetWithJsonPath(string jsonPath, string propertyName, string? newValue, bool suppressLogging = false)
         {
             if (IsReadOnly)
                 return false;
@@ -242,7 +246,7 @@ namespace FileManager
             return true;
         }
 
-        private static string formatValueForLog(string value)
+        private static string formatValueForLog(string? value)
             => value is null ? "[null]"
             : string.IsNullOrEmpty(value) ? "[empty]"
             : string.IsNullOrWhiteSpace(value) ? $"[whitespace. Length={value.Length}]"
@@ -283,7 +287,6 @@ namespace FileManager
         private void createNewFile()
         {
             File.WriteAllText(Filepath, "{}");
-            System.Threading.Thread.Sleep(100);
         }
     }
 }

Source/FileManager/ReplacementCharacters.cs

@@ -5,6 +5,7 @@ using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 
+#nullable enable
 namespace FileManager
 {
 	public record Replacement
@@ -59,7 +60,7 @@ namespace FileManager
 	[JsonConverter(typeof(ReplacementCharactersConverter))]
 	public class ReplacementCharacters
 	{
-		public override bool Equals(object obj)
+		public override bool Equals(object? obj)
 		{
 			if (obj is ReplacementCharacters second && Replacements.Count == second.Replacements.Count)
 			{
@@ -173,7 +174,7 @@ namespace FileManager
 				Path.DirectorySeparatorChar, Path.AltDirectorySeparatorChar
 			}).ToArray();
 
-		public IReadOnlyList<Replacement> Replacements { get; init; }
+		required public IReadOnlyList<Replacement> Replacements { get; init; }
 		private string DefaultReplacement => Replacements[0].ReplacementString;
 		private Replacement ForwardSlash => Replacements[1];
 		private Replacement BackSlash => Replacements[2];
@@ -298,12 +299,14 @@ namespace FileManager
 		public override bool CanConvert(Type objectType)
 			=> objectType == typeof(ReplacementCharacters);
 
-		public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer)
+		public override object ReadJson(JsonReader reader, Type objectType, object? existingValue, JsonSerializer serializer)
 		{
 			var jObj = JObject.Load(reader);
 			var replaceArr = jObj[nameof(Replacement)];
-			IReadOnlyList<Replacement> dict = replaceArr
+			var dict
-				.ToObject<Replacement[]>().ToList();
+				= replaceArr?.ToObject<Replacement[]>()?.ToList()
+				?? ReplacementCharacters.Default.Replacements;
+
 
 			//Ensure that the first 6 replacements are for the expected chars and that all replacement strings are valid.
 			//If not, reset to default.
@@ -325,9 +328,10 @@ namespace FileManager
 			return new ReplacementCharacters { Replacements = dict };
 		}
 
-		public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
+		public override void WriteJson(JsonWriter writer, object? value, JsonSerializer serializer)
 		{
-			ReplacementCharacters replacements = (ReplacementCharacters)value;
+			if (value is not ReplacementCharacters replacements)
+				return;
 
 			var propertyNames = replacements.Replacements
 				.Select(JObject.FromObject).ToList();

Source/LibationFileManager/AudibleFileStorage.cs

@@ -9,11 +9,12 @@ using System.Threading.Tasks;
 using System.Threading;
 using FileManager;
 
+#nullable enable
 namespace LibationFileManager
 {
     public abstract class AudibleFileStorage
     {
-        protected abstract LongPath GetFilePathCustom(string productId);
+        protected abstract LongPath? GetFilePathCustom(string productId);
         protected abstract List<LongPath> GetFilePathsCustom(string productId);
 
         #region static
@@ -57,7 +58,7 @@ namespace LibationFileManager
             regexTemplate = $@"{{0}}.*?\.({extAggr})$";
         }
 
-        protected LongPath GetFilePath(string productId)
+        protected LongPath? GetFilePath(string productId)
         {
             // primary lookup
             var cachedFile = FilePathCache.GetFirstPath(productId, FileType);
@@ -87,7 +88,7 @@ namespace LibationFileManager
     {
         internal AaxcFileStorage() : base(FileType.AAXC) { }
 
-        protected override LongPath GetFilePathCustom(string productId)
+        protected override LongPath? GetFilePathCustom(string productId)
             => GetFilePathsCustom(productId).FirstOrDefault();
 
         protected override List<LongPath> GetFilePathsCustom(string productId)
@@ -104,9 +105,9 @@ namespace LibationFileManager
     public class AudioFileStorage : AudibleFileStorage
     {
         internal AudioFileStorage() : base(FileType.Audio)
-            => BookDirectoryFiles ??= new BackgroundFileSystem(BooksDirectory, "*.*", SearchOption.AllDirectories);
+            => BookDirectoryFiles ??= newBookDirectoryFiles();
 
-        private static BackgroundFileSystem BookDirectoryFiles { get; set; }
+        private static BackgroundFileSystem? BookDirectoryFiles { get; set; }
         private static object bookDirectoryFilesLocker { get; } = new();
 		private static EnumerationOptions enumerationOptions { get; } = new()
 		{
@@ -115,15 +116,18 @@ namespace LibationFileManager
 			MatchCasing = MatchCasing.CaseInsensitive
 		};
 
-		protected override LongPath GetFilePathCustom(string productId)
+		protected override LongPath? GetFilePathCustom(string productId)
             => GetFilePathsCustom(productId).FirstOrDefault();
 
+        private static BackgroundFileSystem newBookDirectoryFiles()
+            => new BackgroundFileSystem(BooksDirectory, "*.*", SearchOption.AllDirectories);
+
 		protected override List<LongPath> GetFilePathsCustom(string productId)
         {
             // If user changed the BooksDirectory: reinitialize
             lock (bookDirectoryFilesLocker)
-                if (BooksDirectory != BookDirectoryFiles.RootDirectory)
+                if (BooksDirectory != BookDirectoryFiles?.RootDirectory)
-                    BookDirectoryFiles = new BackgroundFileSystem(BooksDirectory, "*.*", SearchOption.AllDirectories);
+                    BookDirectoryFiles = newBookDirectoryFiles();
 
 			var regex = GetBookSearchRegex(productId);
 
@@ -138,9 +142,16 @@ namespace LibationFileManager
                 .ToList();
         }
 
-        public void Refresh() => BookDirectoryFiles.RefreshFiles();
+        public void Refresh()
+        {
+            if (BookDirectoryFiles is null)
+                lock (bookDirectoryFilesLocker)
+                    BookDirectoryFiles = newBookDirectoryFiles();
+            else
+                BookDirectoryFiles?.RefreshFiles();
+        }
 
-        public LongPath GetPath(string productId) => GetFilePath(productId);
+        public LongPath? GetPath(string productId) => GetFilePath(productId);
 
 		public static async IAsyncEnumerable<FilePathCache.CacheEntry> FindAudiobooksAsync(LongPath searchDirectory, [EnumeratorCancellation] CancellationToken cancellationToken)
 		{
@@ -151,7 +162,7 @@ namespace LibationFileManager
 				if (cancellationToken.IsCancellationRequested)
 					yield break;
 
-				FilePathCache.CacheEntry audioFile = default;
+				FilePathCache.CacheEntry? audioFile = default;
 
 				try
 				{

Source/LibationFileManager/Configuration.Environment.cs

@@ -4,6 +4,7 @@ using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 
+#nullable enable
 namespace LibationFileManager
 {
 	[Flags]
@@ -20,7 +21,7 @@ namespace LibationFileManager
 		public static bool IsWindows { get; } = OperatingSystem.IsWindows();
         public static bool IsLinux { get; } = OperatingSystem.IsLinux();
         public static bool IsMacOs { get; } = OperatingSystem.IsMacOS();
-		public static Version LibationVersion { get; private set; }
+		public static Version? LibationVersion { get; private set; }
 		public static void SetLibationVersion(Version version) => LibationVersion = version;
 
 		public static OS OS { get; }

Source/LibationFileManager/Configuration.HelpText.cs

@@ -1,6 +1,7 @@
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
 
+#nullable enable
 namespace LibationFileManager
 {
     public partial class Configuration
@@ -29,8 +30,7 @@ namespace LibationFileManager
         }
         .AsReadOnly();
 
-        public static string GetHelpText(string settingName)
+        public static string? GetHelpText(string settingName)
             => HelpText.TryGetValue(settingName, out var value) ? value : null;
-
 	}
 }

Source/LibationFileManager/Configuration.KnownDirectories.cs

@@ -5,11 +5,12 @@ using System.IO;
 using System.Linq;
 using Dinah.Core;
 
+#nullable enable
 namespace LibationFileManager
 {
     public partial class Configuration
     {
-        public static string ProcessDirectory { get; } = Path.GetDirectoryName(Exe.FileLocationOnDisk);
+        public static string ProcessDirectory { get; } = Path.GetDirectoryName(Exe.FileLocationOnDisk)!;
 		public static string AppDir_Relative => $@".{Path.PathSeparator}{LIBATION_FILES_KEY}";
         public static string AppDir_Absolute => Path.GetFullPath(Path.Combine(ProcessDirectory, LIBATION_FILES_KEY));
         public static string MyDocs => Path.GetFullPath(Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), "Libation"));
@@ -36,7 +37,7 @@ namespace LibationFileManager
             LibationFiles = 5
         }
         // use func calls so we always get the latest value of LibationFiles
-        private static List<(KnownDirectories directory, Func<string> getPathFunc)> directoryOptionsPaths { get; } = new()
+        private static List<(KnownDirectories directory, Func<string?> getPathFunc)> directoryOptionsPaths { get; } = new()
         {
             (KnownDirectories.None, () => null),
             (KnownDirectories.UserProfile, () => UserProfile),
@@ -47,7 +48,7 @@ namespace LibationFileManager
 			// also, keep this at bottom of this list
 			(KnownDirectories.LibationFiles, () => libationFilesPathCache)
         };
-        public static string GetKnownDirectoryPath(KnownDirectories directory)
+        public static string? GetKnownDirectoryPath(KnownDirectories directory)
         {
             var dirFunc = directoryOptionsPaths.SingleOrDefault(dirFunc => dirFunc.directory == directory);
             return dirFunc == default ? null : dirFunc.getPathFunc();

Source/LibationFileManager/Configuration.LibationFiles.cs

@@ -7,6 +7,7 @@ using Newtonsoft.Json;
 using Serilog;
 using Dinah.Core.Logging;
 
+#nullable enable
 namespace LibationFileManager
 {
     public partial class Configuration
@@ -44,7 +45,7 @@ namespace LibationFileManager
             }
         }
 
-        private static string libationFilesPathCache { get; set; }
+        private static string? libationFilesPathCache { get; set; }
 
 		/// <summary>
 		/// Try to find appsettings.json in the following locations:
@@ -124,7 +125,10 @@ namespace LibationFileManager
             // do not check whether directory exists. special/meta directory (eg: AppDir) is valid
             // verify from live file. no try/catch. want failures to be visible
             var jObjFinal = JObject.Parse(File.ReadAllText(AppsettingsJsonFile));
-            var valueFinal = jObjFinal[LIBATION_FILES_KEY].Value<string>();
+
+			if (jObjFinal[LIBATION_FILES_KEY]?.Value<string>() is not string valueFinal)
+				throw new InvalidDataException($"{LIBATION_FILES_KEY} not found in {AppsettingsJsonFile}");
+
             return valueFinal;
         }
 

Source/LibationFileManager/Configuration.Logging.cs

@@ -1,19 +1,18 @@
 using System;
-using System.Collections.Generic;
 using System.ComponentModel;
 using System.Linq;
-using Dinah.Core;
 using Dinah.Core.Logging;
 using FileManager;
 using Microsoft.Extensions.Configuration;
 using Serilog;
 using Serilog.Events;
 
+#nullable enable
 namespace LibationFileManager
 {
     public partial class Configuration
     {
-        private IConfigurationRoot configuration;
+        private IConfigurationRoot? configuration;
 
         public void ConfigureLogging()
         {
@@ -31,20 +30,20 @@ namespace LibationFileManager
         {
             get
             {
-                var logLevelStr = persistentDictionary.GetStringFromJsonPath("Serilog", "MinimumLevel");
+                var logLevelStr = Settings.GetStringFromJsonPath("Serilog", "MinimumLevel");
                 return Enum.TryParse<LogEventLevel>(logLevelStr, out var logLevelEnum) ? logLevelEnum : LogEventLevel.Information;
             }
             set
             {
                 OnPropertyChanging(nameof(LogLevel), LogLevel, value);
-                var valueWasChanged = persistentDictionary.SetWithJsonPath("Serilog", "MinimumLevel", value.ToString());
+                var valueWasChanged = Settings.SetWithJsonPath("Serilog", "MinimumLevel", value.ToString());
                 if (!valueWasChanged)
                 {
                     Log.Logger.Debug("LogLevel.set attempt. No change");
                     return;
                 }
 
-                configuration.Reload();
+                configuration?.Reload();
 
                 OnPropertyChanged(nameof(LogLevel), value);
 

Source/LibationFileManager/Configuration.PersistentSettings.cs

@@ -1,6 +1,7 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using System.Runtime.CompilerServices;
@@ -8,6 +9,7 @@ using FileManager;
 using Newtonsoft.Json;
 using Newtonsoft.Json.Converters;
 
+#nullable enable
 namespace LibationFileManager
 {
 	public partial class Configuration
@@ -18,34 +20,52 @@ namespace LibationFileManager
 		// config class is only responsible for path. not responsible for setting defaults, dir validation, or dir creation
 		// exceptions: appsettings.json, LibationFiles dir, Settings.json
 
-		private PersistentDictionary persistentDictionary;
+		private PersistentDictionary? persistentDictionary;
 
-		public bool RemoveProperty(string propertyName) => persistentDictionary.RemoveProperty(propertyName);
+		private PersistentDictionary Settings
+		{
+			get
+			{
+				if (persistentDictionary is null)
+					throw new InvalidOperationException($"{nameof(persistentDictionary)} must first be set by accessing {nameof(LibationFiles)} or calling {nameof(SettingsFileIsValid)}");
+				return persistentDictionary;
+			}
+		}
 
-		public T GetNonString<T>(T defaultValue, [CallerMemberName] string propertyName = "") => persistentDictionary.GetNonString(propertyName, defaultValue);
+		public bool RemoveProperty(string propertyName) => Settings.RemoveProperty(propertyName);
-		public object GetObject([CallerMemberName] string propertyName = "") => persistentDictionary.GetObject(propertyName);
+
-		public string GetString(string defaultValue = null, [CallerMemberName] string propertyName = "") => persistentDictionary.GetString(propertyName, defaultValue);
+		[return: NotNullIfNotNull(nameof(defaultValue))]
-		public void SetNonString(object newValue, [CallerMemberName] string propertyName = "")
+		public T? GetNonString<T>(T defaultValue, [CallerMemberName] string propertyName = "")
+			=> Settings.GetNonString(propertyName, defaultValue);
+
+
+		[return: NotNullIfNotNull(nameof(defaultValue))]
+		public string? GetString(string? defaultValue = null, [CallerMemberName] string propertyName = "")
+			=> Settings.GetString(propertyName, defaultValue);
+
+		public object? GetObject([CallerMemberName] string propertyName = "") => Settings.GetObject(propertyName);
+
+		public void SetNonString(object? newValue, [CallerMemberName] string propertyName = "")
 		{
 			var existing = getExistingValue(propertyName);
 			if (existing?.Equals(newValue) is true) return;
 
 			OnPropertyChanging(propertyName, existing, newValue);
-			persistentDictionary.SetNonString(propertyName, newValue);
+			Settings.SetNonString(propertyName, newValue);
 			OnPropertyChanged(propertyName, newValue);
 		}
 
-		public void SetString(string newValue, [CallerMemberName] string propertyName = "")
+		public void SetString(string? newValue, [CallerMemberName] string propertyName = "")
 		{
 			var existing = getExistingValue(propertyName);
 			if (existing?.Equals(newValue) is true) return;
 
 			OnPropertyChanging(propertyName, existing, newValue);
-			persistentDictionary.SetString(propertyName, newValue);
+			Settings.SetString(propertyName, newValue);
 			OnPropertyChanged(propertyName, newValue);
 		}
 
-		private object getExistingValue(string propertyName)
+		private object? getExistingValue(string propertyName)
 		{
 			var property = GetType().GetProperty(propertyName);
 			if (property is not null) return property.GetValue(this);
@@ -53,16 +73,16 @@ namespace LibationFileManager
 		}
 
 		/// <summary>WILL ONLY set if already present. WILL NOT create new</summary>
-		public void SetWithJsonPath(string jsonPath, string propertyName, string newValue, bool suppressLogging = false)
+		public void SetWithJsonPath(string jsonPath, string propertyName, string? newValue, bool suppressLogging = false)
 		{
-			var settingWasChanged = persistentDictionary.SetWithJsonPath(jsonPath, propertyName, newValue, suppressLogging);
+			var settingWasChanged = Settings.SetWithJsonPath(jsonPath, propertyName, newValue, suppressLogging);
 			if (settingWasChanged)
 				configuration?.Reload();
 		}
 
 		public string SettingsFilePath => Path.Combine(LibationFiles, "Settings.json");
 
-		public static string GetDescription(string propertyName)
+		public static string? GetDescription(string propertyName)
 		{
 			var attribute = typeof(Configuration)
 				.GetProperty(propertyName)
@@ -73,7 +93,7 @@ namespace LibationFileManager
 			return attribute?.Description;
 		}
 
-		public bool Exists(string propertyName) => persistentDictionary.Exists(propertyName);
+		public bool Exists(string propertyName) => Settings.Exists(propertyName);
 
 		[Description("Set cover art as the folder's icon.")]
 		public bool UseCoverAsFolderIcon { get => GetNonString(defaultValue: false); set => SetNonString(value); }
@@ -91,7 +111,7 @@ namespace LibationFileManager
 		public bool BetaOptIn { get => GetNonString(defaultValue: false); set => SetNonString(value); }
 
 		[Description("Location for book storage. Includes destination of newly liberated books")]
-		public LongPath Books { get => GetString(); set => SetString(value); }
+		public LongPath? Books { get => GetString(); set => SetString(value); }
 
 		[Description("Overwrite existing files if they already exist?")]
 		public bool OverwriteExisting { get => GetNonString(defaultValue: false); set => SetNonString(value); }

Source/LibationFileManager/Configuration.PropertyChange.cs

@@ -1,5 +1,6 @@
 using System.Collections.Generic;
 
+#nullable enable
 namespace LibationFileManager
 {
 	public partial class Configuration
@@ -9,17 +10,17 @@ namespace LibationFileManager
 		 * and be sure to clone it before returning. This allows Configuration to
 		 * accurately detect if any of the Dictionary's elements have changed.
 		 */
-		private class EquatableDictionary<TKey, TValue> : Dictionary<TKey, TValue>
+		private class EquatableDictionary<TKey, TValue> : Dictionary<TKey, TValue> where TKey : notnull
 		{
 			public EquatableDictionary() { }
 			public EquatableDictionary(IEnumerable<KeyValuePair<TKey, TValue>> keyValuePairs) : base(keyValuePairs) { }
 			public EquatableDictionary<TKey, TValue> Clone() => new(this);
-			public override bool Equals(object obj)
+			public override bool Equals(object? obj)
 			{
 				if (obj is Dictionary<TKey, TValue> dic && Count == dic.Count)
 				{
 					foreach (var pair in this)
-						if (!dic.TryGetValue(pair.Key, out var value) || !pair.Value.Equals(value))
+						if (!dic.TryGetValue(pair.Key, out var value) || pair.Value?.Equals(value) is not true)
 							return false;
 
 					return true;

Source/LibationFileManager/Configuration.cs

@@ -4,7 +4,7 @@ using System.Linq;
 using Dinah.Core;
 using FileManager;
 
-
+#nullable enable
 namespace LibationFileManager
 {
 	public partial class Configuration : PropertyChangeFilter
@@ -24,9 +24,12 @@ namespace LibationFileManager
 
 			if (!Directory.Exists(booksDir))
 			{
+				if (Path.GetDirectoryName(settingsFile) is not string dir)
+					throw new DirectoryNotFoundException(settingsFile);
+
 				//"Books" is not null, so setup has already been run.
 				//Since Books can't be found, try to create it in Libation settings folder
-				booksDir = Path.Combine(Path.GetDirectoryName(settingsFile), nameof(Books));
+				booksDir = Path.Combine(dir, nameof(Books));
 				try
 				{
 					Directory.CreateDirectory(booksDir);

Source/LibationFileManager/FilePathCache.cs

@@ -6,6 +6,7 @@ using Dinah.Core.Collections.Immutable;
 using FileManager;
 using Newtonsoft.Json;
 
+#nullable enable
 namespace LibationFileManager
 {
 	public static class FilePathCache
@@ -14,8 +15,8 @@ namespace LibationFileManager
 
 		private const string FILENAME = "FileLocations.json";
 
-		public static event EventHandler<CacheEntry> Inserted;
+		public static event EventHandler<CacheEntry>? Inserted;
-		public static event EventHandler<CacheEntry> Removed;
+		public static event EventHandler<CacheEntry>? Removed;
 
 		private static Cache<CacheEntry> cache { get; } = new Cache<CacheEntry>();
 
@@ -51,7 +52,7 @@ namespace LibationFileManager
 			.Select(entry => (entry.FileType, entry.Path))
 			.ToList();
 
-		public static LongPath GetFirstPath(string id, FileType type)
+		public static LongPath? GetFirstPath(string id, FileType type)
 			=> getEntries(entry => entry.Id == id && entry.FileType == type)
 			?.FirstOrDefault()
 			?.Path;

Source/LibationFileManager/IInteropFunctions.cs

@@ -2,9 +2,9 @@
 using System.Diagnostics;
 using System.Threading.Tasks;
 
+#nullable enable
 namespace LibationFileManager
 {
-#nullable enable
 	public interface IInteropFunctions
     {
 		/// <summary>

Source/LibationFileManager/InteropFactory.cs

@@ -5,11 +5,12 @@ using System.Linq;
 using System.Reflection;
 using Dinah.Core;
 
+#nullable enable
 namespace LibationFileManager
 {
     public static class InteropFactory
     {
-        public static Type InteropFunctionsType { get; }
+        public static Type? InteropFunctionsType { get; }
 
         public static IInteropFunctions Create() => _create();
 
@@ -17,13 +18,17 @@ namespace LibationFileManager
         //public static IInteropFunctions Create(string str, int i) => _create(str, i);
         //public static IInteropFunctions Create(params object[] values) => _create(values);
 
-        private static IInteropFunctions instance { get; set; }
+        private static IInteropFunctions? instance { get; set; }
         private static IInteropFunctions _create(params object[] values)
         {
             instance ??=
                 InteropFunctionsType is null
                 ? new NullInteropFunctions()
                 : Activator.CreateInstance(InteropFunctionsType, values) as IInteropFunctions;
+
+            if (instance is null)
+                throw new TypeLoadException();
+
             return instance;
         }
 
@@ -66,7 +71,7 @@ namespace LibationFileManager
                 .GetTypes()
                 .FirstOrDefault(type.IsAssignableFrom);
         }
-        private static string getOSConfigApp()
+        private static string? getOSConfigApp()
         {
             // find '*ConfigApp.dll' files
             var appName =
@@ -76,8 +81,8 @@ namespace LibationFileManager
             return appName;
         }
 
-        private static Dictionary<string, Assembly> lowEffortCache { get; } = new();
+        private static Dictionary<string, Assembly?> lowEffortCache { get; } = new();
-        private static Assembly CurrentDomain_AssemblyResolve(object sender, ResolveEventArgs args)
+        private static Assembly? CurrentDomain_AssemblyResolve(object? sender, ResolveEventArgs args)
         {
             var asmName = new AssemblyName(args.Name);
             var here = Configuration.ProcessDirectory;
@@ -97,7 +102,7 @@ namespace LibationFileManager
             return assembly;
         }
 
-		private static Assembly CurrentDomain_AssemblyResolve_internal(AssemblyName asmName, string here)
+		private static Assembly? CurrentDomain_AssemblyResolve_internal(AssemblyName asmName, string here)
         {
             /*
              * Find the requested assembly in the program files directory.

Source/LibationFileManager/LibraryBookDto.cs

@@ -2,26 +2,27 @@
 using System.Collections.Generic;
 using System.Linq;
 
+#nullable enable
 namespace LibationFileManager
 {
     public class BookDto
     {
-        public string AudibleProductId { get; set; }
+        public string? AudibleProductId { get; set; }
-        public string Title { get; set; }
+        public string? Title { get; set; }
-		public string Subtitle { get; set; }
+		public string? Subtitle { get; set; }
-		public string TitleWithSubtitle { get; set; }
+		public string? TitleWithSubtitle { get; set; }
-		public string Locale { get; set; }
+		public string? Locale { get; set; }
         public int? YearPublished { get; set; }
 
-        public IEnumerable<string> Authors { get; set; }
+        public IEnumerable<string>? Authors { get; set; }
-        public string AuthorNames => string.Join(", ", Authors);
+        public string? AuthorNames => Authors is null ? null : string.Join(", ", Authors);
-        public string FirstAuthor => Authors.FirstOrDefault();
+        public string? FirstAuthor => Authors?.FirstOrDefault();
 
-        public IEnumerable<string> Narrators { get; set; }
+        public IEnumerable<string>? Narrators { get; set; }
-        public string NarratorNames => string.Join(", ", Narrators);
+        public string? NarratorNames => Narrators is null? null: string.Join(", ", Narrators);
-        public string FirstNarrator => Narrators.FirstOrDefault();
+        public string? FirstNarrator => Narrators?.FirstOrDefault();
 
-        public string SeriesName { get; set; }
+        public string? SeriesName { get; set; }
         public float? SeriesNumber { get; set; }
         public bool IsSeries => !string.IsNullOrEmpty(SeriesName);
         public bool IsPodcastParent { get; set; }
@@ -32,13 +33,13 @@ namespace LibationFileManager
         public int Channels { get; set; }
 		public DateTime FileDate { get; set; } = DateTime.Now;
         public DateTime? DatePublished { get; set; }
-        public string Language { get; set; }
+        public string? Language { get; set; }
 	}
 
     public class LibraryBookDto : BookDto
 	{
 		public DateTime? DateAdded { get; set; }
-		public string Account { get; set; }
+		public string? Account { get; set; }
-		public string AccountNickname { get; set; }
+		public string? AccountNickname { get; set; }
     }
 }

Source/LibationFileManager/NameListFormat.cs

@@ -5,12 +5,15 @@ using System.Collections.Generic;
 using System.Linq;
 using System.Text.RegularExpressions;
 
+#nullable enable
 namespace LibationFileManager
 {
 	internal partial class NameListFormat
 	{
-		public static string Formatter(ITemplateTag _, IEnumerable<string> names, string formatString)
+		public static string Formatter(ITemplateTag _, IEnumerable<string>? names, string formatString)
 		{
+			if (names is null) return "";
+
             var humanNames = names.Select(n => new HumanName(RemoveSuffix(n), Prefer.FirstOverPrefix));
 
 			var sortedNames = Sort(humanNames, formatString);

Source/LibationFileManager/NullInteropFunctions.cs

@@ -2,7 +2,6 @@
 using System.Diagnostics;
 
 #nullable enable
-
 namespace LibationFileManager
 {
     public class NullInteropFunctions : IInteropFunctions

Source/LibationFileManager/PictureStorage.cs

@@ -6,18 +6,25 @@ using System.Linq;
 using System.Net.Http;
 using System.Threading.Tasks;
 
+#nullable enable
 namespace LibationFileManager
 {
 	public enum PictureSize { Native, _80x80 = 80, _300x300 = 300, _500x500 = 500 }
 	public class PictureCachedEventArgs : EventArgs
 	{
-		public PictureDefinition Definition { get; internal set; }
+		public PictureDefinition Definition { get; }
-		public byte[] Picture { get; internal set; }
+		public byte[] Picture { get; }
+
+		internal PictureCachedEventArgs(PictureDefinition definition, byte[] picture)
+		{
+			Definition = definition;
+			Picture = picture;
+		}
 	}
 	public struct PictureDefinition : IEquatable<PictureDefinition>
 	{
-		public string PictureId { get; }
+		public string PictureId { get; init; }
-		public PictureSize Size { get; }
+		public PictureSize Size { get; init; }
 
 		public PictureDefinition(string pictureId, PictureSize pictureSize)
 		{
@@ -45,7 +52,7 @@ namespace LibationFileManager
 			.Start();
 		}
 
-		public static event EventHandler<PictureCachedEventArgs> PictureCached;
+		public static event EventHandler<PictureCachedEventArgs>? PictureCached;
 
 		private static BlockingCollection<PictureDefinition> DownloadQueue { get; } = new BlockingCollection<PictureDefinition>();
 		private static object cacheLocker { get; } = new object();
@@ -112,7 +119,7 @@ namespace LibationFileManager
 				lock (cacheLocker)
 					cache[def] = bytes;
 
-				PictureCached?.Invoke(nameof(PictureStorage), new PictureCachedEventArgs { Definition = def, Picture = bytes });
+				PictureCached?.Invoke(nameof(PictureStorage), new PictureCachedEventArgs(def, bytes));
 			}
 		}
 

Source/LibationFileManager/QuickFilters.cs

@@ -5,11 +5,14 @@ using System.Linq;
 using Dinah.Core.Collections.Generic;
 using Newtonsoft.Json;
 
+#nullable enable
 namespace LibationFileManager
 {
     public static class QuickFilters
     {
-        public static event EventHandler Updated;
+        public static event EventHandler? Updated;
+
+		public static event EventHandler? UseDefaultChanged;
 
 		internal class FilterState
         {
@@ -17,18 +20,15 @@ namespace LibationFileManager
             public List<string> Filters { get; set; } = new List<string>();
         }
 
-        static FilterState inMemoryState { get; } = new FilterState();
-
         public static string JsonFile => Path.Combine(Configuration.Instance.LibationFiles, "QuickFilters.json");
 
-        static QuickFilters()
-        {
-            // load json into memory. if file doesn't exist, nothing to do. save() will create if needed
-            if (File.Exists(JsonFile))
-                inMemoryState = JsonConvert.DeserializeObject<FilterState>(File.ReadAllText(JsonFile));
-        }
 
-        public static event EventHandler UseDefaultChanged;
+		// load json into memory. if file doesn't exist, nothing to do. save() will create if needed
+		static FilterState inMemoryState { get; }
+            = File.Exists(JsonFile) && JsonConvert.DeserializeObject<FilterState>(File.ReadAllText(JsonFile)) is FilterState inMemState
+            ? inMemState
+            : new FilterState();
+
         public static bool UseDefault
         {
             get => inMemoryState.UseDefault;
@@ -43,7 +43,7 @@ namespace LibationFileManager
                     save(false);
                 }
 
-                UseDefaultChanged?.Invoke(null, null);
+                UseDefaultChanged?.Invoke(null, EventArgs.Empty);
             }
         }
 
@@ -121,7 +121,7 @@ namespace LibationFileManager
 			}
 
             if (invokeUpdatedEvent)
-                Updated?.Invoke(null, null);
+                Updated?.Invoke(null, EventArgs.Empty);
         }
     }
 }

Source/LibationFileManager/TemplateEditor[T].cs

@@ -4,6 +4,7 @@ using System.Collections.Generic;
 using System;
 using System.IO;
 
+#nullable enable
 namespace LibationFileManager
 {
 	public interface ITemplateEditor
@@ -14,14 +15,11 @@ namespace LibationFileManager
 		string DefaultTemplate { get; }
 		string TemplateName { get; }
 		string TemplateDescription { get; }
-		Templates Folder { get; }
-		Templates File { get; }
-		Templates Name { get; }
 		Templates EditingTemplate { get; }
-		void SetTemplateText(string templateText);
+		bool SetTemplateText(string templateText);
-		string GetFolderName();
+		string? GetFolderName();
-		string GetFileName();
+		string? GetFileName();
-		string GetName();
+		string? GetName();
 	}
 
 	public class TemplateEditor<T> : ITemplateEditor where T : Templates, ITemplate, new()
@@ -32,9 +30,9 @@ namespace LibationFileManager
 		public string DefaultTemplate { get; private init; }
 		public string TemplateName { get; private init; }
 		public string TemplateDescription { get; private init; }
-		public Templates Folder { get; private set; }
+		private Templates? Folder { get; set; }
-		public Templates File { get; private set; }
+		private Templates? File { get; set; }
-		public Templates Name { get; private set; }
+		private Templates? Name { get; set; }
 		public Templates EditingTemplate
 		{
 			get => _editingTemplate;
@@ -43,10 +41,14 @@ namespace LibationFileManager
 
 		private Templates _editingTemplate;
 
-		public void SetTemplateText(string templateText)
+		public bool SetTemplateText(string templateText)
+		{
+			if (Templates.TryGetTemplate<T>(templateText, out var template))
 			{
-			Templates.TryGetTemplate<T>(templateText, out var template);
 				EditingTemplate = template;
+				return true;
+			}
+			return false;
 		}
 
 		private static readonly LibraryBookDto libraryBookDto
@@ -80,7 +82,7 @@ namespace LibationFileManager
 				Title = "A Flight for Life"
 			};
 
-		public string GetFolderName()
+		public string? GetFolderName()
 		{
 			/*
 			* Path must be rooted for windows to allow long file paths. This is
@@ -88,49 +90,49 @@ namespace LibationFileManager
 			* subdirectories. Without rooting, we won't be allowed to create a
 			* relative path longer than MAX_PATH.
 			*/
-			var dir = Folder.GetFilename(libraryBookDto, BaseDirectory, "");
+			var dir = Folder?.GetFilename(libraryBookDto, BaseDirectory, "");
+			if (dir is null) return null;
 			return Path.GetRelativePath(BaseDirectory, dir);
 		}
 
-		public string GetFileName()
+		public string? GetFileName()
-			=> File.GetFilename(libraryBookDto, partFileProperties, "", "");
+			=> File?.GetFilename(libraryBookDto, partFileProperties, "", "");
-		public string GetName()
+		public string? GetName()
-			=> Name.GetName(libraryBookDto, partFileProperties);
+			=> Name?.GetName(libraryBookDto, partFileProperties);
+
+		private TemplateEditor(
+			Templates editingTemplate,
+			LongPath baseDirectory,
+			string defaultTemplate,
+			string templateName,
+			string templateDescription)
+		{
+			_editingTemplate = editingTemplate;
+			BaseDirectory = baseDirectory;
+			DefaultTemplate = defaultTemplate;
+			TemplateName = templateName;
+			TemplateDescription = templateDescription;
+		}
 
 		public static ITemplateEditor CreateFilenameEditor(LongPath baseDir, string templateText)
 		{
-			Templates.TryGetTemplate<T>(templateText, out var template);
+			if (!Templates.TryGetTemplate<T>(templateText, out var template))
+				throw new ArgumentException($"Failed to parse {nameof(templateText)}");
 
-			var templateEditor = new TemplateEditor<T>
+			var templateEditor = new TemplateEditor<T>(template, baseDir, T.DefaultTemplate, T.Name, T.Description);
-			{
-				_editingTemplate = template,
-				BaseDirectory = baseDir,
-				DefaultTemplate = T.DefaultTemplate,
-				TemplateName = T.Name,
-				TemplateDescription = T.Description
-				
-			};
 
 			if (!templateEditor.IsFolder && !templateEditor.IsFilePath)
 				throw new InvalidOperationException($"This method is only for File and Folder templates. Use {nameof(CreateNameEditor)} for name templates");
 
-			templateEditor.Folder = templateEditor.IsFolder ? template : Templates.Folder;
-			templateEditor.File = templateEditor.IsFolder ? Templates.File : template;
-
 			return templateEditor;
 		}
 
 		public static ITemplateEditor CreateNameEditor(string templateText)
 		{
-			Templates.TryGetTemplate<T>(templateText, out var nameTemplate);
+			if (!Templates.TryGetTemplate<T>(templateText, out var nameTemplate))
+				throw new ArgumentException($"Failed to parse {nameof(templateText)}");
 
-			var templateEditor = new TemplateEditor<T>
+			var templateEditor = new TemplateEditor<T>(nameTemplate, "", T.DefaultTemplate, T.Name, T.Description);
-			{
-				_editingTemplate = nameTemplate,
-				DefaultTemplate = T.DefaultTemplate,
-				TemplateName = T.Name,
-				TemplateDescription = T.Description
-			};
 
 			if (templateEditor.IsFolder || templateEditor.IsFilePath)
 				throw new InvalidOperationException($"This method is only for name templates. Use {nameof(CreateFilenameEditor)} for file templates");

Source/LibationFileManager/TemplateTags.cs

@@ -1,5 +1,6 @@
 using FileManager.NamingTemplate;
 
+#nullable enable
 namespace LibationFileManager
 {
 	public sealed class TemplateTags : ITemplateTag
@@ -10,7 +11,7 @@ namespace LibationFileManager
 		public string Description { get; }
 		public string Display { get; }
 
-		private TemplateTags(string tagName, string description, string defaultValue = null, string display = null)
+		private TemplateTags(string tagName, string description, string? defaultValue = null, string? display = null)
 		{
 			TagName = tagName;
 			Description = description;

Source/LibationFileManager/Templates.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.IO;
 using System.Linq;
 using AaxDecrypter;
@@ -8,6 +9,7 @@ using FileManager;
 using FileManager.NamingTemplate;
 using NameParser;
 
+#nullable enable
 namespace LibationFileManager
 {
 	public interface ITemplate
@@ -26,10 +28,10 @@ namespace LibationFileManager
 		//Assigning the properties in the static constructor will require all
 		//Templates users to have a valid configuration file. To allow tests
 		//to work without access to Configuration, only load templates on demand.
-		private static FolderTemplate _folder;
+		private static FolderTemplate? _folder;
-		private static FileTemplate _file;
+		private static FileTemplate? _file;
-		private static ChapterFileTemplate _chapterFile;
+		private static ChapterFileTemplate? _chapterFile;
-		private static ChapterTitleTemplate _chapterTitle;
+		private static ChapterTitleTemplate? _chapterTitle;
 
 		public static FolderTemplate Folder => _folder ??= GetTemplate<FolderTemplate>(Configuration.Instance.FolderTemplate);
 		public static FileTemplate File => _file ??= GetTemplate<FileTemplate>(Configuration.Instance.FileTemplate);
@@ -38,10 +40,10 @@ namespace LibationFileManager
 
 		#region Template Parsing
 
-		public static T GetTemplate<T>(string templateText) where T : Templates, ITemplate, new()
+		public static T GetTemplate<T>(string? templateText) where T : Templates, ITemplate, new()
-			=> TryGetTemplate<T>(templateText, out var template) ? template : GetDefaultTemplate<T>();
+			=> TryGetTemplate<T>(templateText ?? "", out var template) ? template : GetDefaultTemplate<T>();
 
-		public static bool TryGetTemplate<T>(string templateText, out T template) where T : Templates, ITemplate, new()
+		public static bool TryGetTemplate<T>(string templateText, [NotNullWhen(true)] out T? template) where T : Templates, ITemplate, new()
 		{
 			var namingTemplate = NamingTemplate.Parse(templateText, T.TagCollections);
 
@@ -56,19 +58,19 @@ namespace LibationFileManager
 		{
 			Configuration.Instance.PropertyChanged +=
 				[PropertyChangeFilter(nameof(Configuration.FolderTemplate))]
-				(_,e) => _folder = GetTemplate<FolderTemplate>((string)e.NewValue);
+				(_,e) => _folder = GetTemplate<FolderTemplate>(e.NewValue as string);
 
 			Configuration.Instance.PropertyChanged +=
 				[PropertyChangeFilter(nameof(Configuration.FileTemplate))]
-				(_, e) => _file = GetTemplate<FileTemplate>((string)e.NewValue);
+				(_, e) => _file = GetTemplate<FileTemplate>(e.NewValue as string);
 
 			Configuration.Instance.PropertyChanged +=
 				[PropertyChangeFilter(nameof(Configuration.ChapterFileTemplate))]
-				(_, e) => _chapterFile = GetTemplate<ChapterFileTemplate>((string)e.NewValue);
+				(_, e) => _chapterFile = GetTemplate<ChapterFileTemplate>(e.NewValue as string);
 
 			Configuration.Instance.PropertyChanged +=
 				[PropertyChangeFilter(nameof(Configuration.ChapterTitleTemplate))]
-				(_, e) => _chapterTitle = GetTemplate<ChapterTitleTemplate>((string)e.NewValue);
+				(_, e) => _chapterTitle = GetTemplate<ChapterTitleTemplate>(e.NewValue as string);
 
 			HumanName.Suffixes.Add("ret");
 			HumanName.Titles.Add("professor");
@@ -78,10 +80,18 @@ namespace LibationFileManager
 
 		#region Template Properties
 
-		public IEnumerable<TemplateTags> TagsRegistered => NamingTemplate.TagsRegistered.Cast<TemplateTags>();
+		public IEnumerable<TemplateTags> TagsRegistered
-		public IEnumerable<TemplateTags> TagsInUse => NamingTemplate.TagsInUse.Cast<TemplateTags>();
+			=> NamingTemplate?.TagsRegistered.Cast<TemplateTags>() ?? Enumerable.Empty<TemplateTags>();
-		public string TemplateText => NamingTemplate.TemplateText;
+		public IEnumerable<TemplateTags> TagsInUse
-		protected NamingTemplate NamingTemplate { get; private set; }
+			=> NamingTemplate?.TagsInUse.Cast<TemplateTags>() ?? Enumerable.Empty<TemplateTags>();
+		public string TemplateText => NamingTemplate?.TemplateText ?? "";
+
+		private readonly NamingTemplate? _namingTemplate;
+		protected NamingTemplate NamingTemplate
+		{
+			get => _namingTemplate ?? throw new NullReferenceException(nameof(_namingTemplate));
+			private init => _namingTemplate = value;
+		}
 
 		#endregion
 
@@ -104,7 +114,7 @@ namespace LibationFileManager
 			return string.Concat(NamingTemplate.Evaluate(libraryBookDto, multiChapProps).Select(p => p.Value));
 		}
 
-		public LongPath GetFilename(LibraryBookDto libraryBookDto, string baseDir, string fileExtension, ReplacementCharacters replacements = null, bool returnFirstExisting = false)
+		public LongPath GetFilename(LibraryBookDto libraryBookDto, string baseDir, string fileExtension, ReplacementCharacters? replacements = null, bool returnFirstExisting = false)
 		{
 			ArgumentValidator.EnsureNotNull(libraryBookDto, nameof(libraryBookDto));
 			ArgumentValidator.EnsureNotNull(baseDir, nameof(baseDir));
@@ -114,7 +124,7 @@ namespace LibationFileManager
 			return GetFilename(baseDir, fileExtension,replacements, returnFirstExisting, libraryBookDto);
 		}
 
-		public LongPath GetFilename(LibraryBookDto libraryBookDto, MultiConvertFileProperties multiChapProps, string baseDir, string fileExtension, ReplacementCharacters replacements = null, bool returnFirstExisting = false)
+		public LongPath GetFilename(LibraryBookDto libraryBookDto, MultiConvertFileProperties multiChapProps, string baseDir, string fileExtension, ReplacementCharacters? replacements = null, bool returnFirstExisting = false)
 		{
 			ArgumentValidator.EnsureNotNull(libraryBookDto, nameof(libraryBookDto));
 			ArgumentValidator.EnsureNotNull(multiChapProps, nameof(multiChapProps));
@@ -246,7 +256,7 @@ namespace LibationFileManager
 			new(caseSensative: true, StringFormatter, DateTimeFormatter, IntegerFormatter, FloatFormatter)
 		{
 			//Don't allow formatting of Id
-			{ TemplateTags.Id, lb => lb.AudibleProductId, v => v },
+			{ TemplateTags.Id, lb => lb.AudibleProductId, v => v ?? "" },
 			{ TemplateTags.Title, lb => lb.TitleWithSubtitle },
 			{ TemplateTags.TitleShort, lb => getTitleShort(lb.Title) },
 			{ TemplateTags.AudibleTitle, lb => lb.Title },
@@ -308,13 +318,13 @@ namespace LibationFileManager
 
 		#region Tag Formatters
 
-		private static string getTitleShort(string title)
+		private static string? getTitleShort(string? title)
 			=> title?.IndexOf(':') > 0 ? title.Substring(0, title.IndexOf(':')) : title;
 
-		private static string getLanguageShort(string language)
+		private static string getLanguageShort(string? language)
 		{
 			if (language is null)
-				return null;
+				return "";
 
 			language = language.Trim();
 			if (language.Length <= 3)
@@ -324,8 +334,9 @@ namespace LibationFileManager
 
 		private static string StringFormatter(ITemplateTag templateTag, string value, string formatString)
 		{
-			if (string.Compare(formatString, "u", ignoreCase: true) == 0) return value?.ToUpper();
+			if (value is null) return "";
-			else if (string.Compare(formatString, "l", ignoreCase: true) == 0) return value?.ToLower();
+			else if (string.Compare(formatString, "u", ignoreCase: true) == 0) return value.ToUpper();
+			else if (string.Compare(formatString, "l", ignoreCase: true) == 0) return value.ToLower();
 			else return value;
 		}
 
@@ -358,7 +369,7 @@ namespace LibationFileManager
 		public class FolderTemplate : Templates, ITemplate
 		{
 			public static string Name { get; }= "Folder Template";
-			public static string Description { get; } = Configuration.GetDescription(nameof(Configuration.FolderTemplate));
+			public static string Description { get; } = Configuration.GetDescription(nameof(Configuration.FolderTemplate)) ?? "";
 			public static string DefaultTemplate { get; } = "<title short> [<id>]";
 			public static IEnumerable<TagCollection> TagCollections
 				=> new TagCollection[] { filePropertyTags, conditionalTags, folderConditionalTags };
@@ -378,7 +389,7 @@ namespace LibationFileManager
 		public class FileTemplate : Templates, ITemplate
 		{
 			public static string Name { get; } = "File Template";
-			public static string Description { get; } = Configuration.GetDescription(nameof(Configuration.FileTemplate));
+			public static string Description { get; } = Configuration.GetDescription(nameof(Configuration.FileTemplate)) ?? "";
 			public static string DefaultTemplate { get; } = "<title> [<id>]";
 			public static IEnumerable<TagCollection> TagCollections { get; } = new TagCollection[] { filePropertyTags, conditionalTags };
 		}
@@ -386,7 +397,7 @@ namespace LibationFileManager
 		public class ChapterFileTemplate : Templates, ITemplate
 		{
 			public static string Name { get; } = "Chapter File Template";
-			public static string Description { get; } = Configuration.GetDescription(nameof(Configuration.ChapterFileTemplate));
+			public static string Description { get; } = Configuration.GetDescription(nameof(Configuration.ChapterFileTemplate)) ?? "";
 			public static string DefaultTemplate { get; } = "<title> [<id>] - <ch# 0> - <ch title>";
 			public static IEnumerable<TagCollection> TagCollections { get; } = chapterPropertyTags.Append(filePropertyTags).Append(conditionalTags);
 
@@ -399,7 +410,7 @@ namespace LibationFileManager
 		public class ChapterTitleTemplate : Templates, ITemplate
 		{
 			public static string Name { get; } = "Chapter Title Template";
-			public static string Description { get; } = Configuration.GetDescription(nameof(Configuration.ChapterTitleTemplate));
+			public static string Description { get; } = Configuration.GetDescription(nameof(Configuration.ChapterTitleTemplate)) ?? "";
 			public static string DefaultTemplate => "<ch#> - <title short>: <ch title>";
 			public static IEnumerable<TagCollection> TagCollections { get; } = chapterPropertyTags.Append(conditionalTags);