Replaced [NotNull, DisallowNull] with null-forgiving operator

The Roslyn code analyzers will throw a `CS8616` if a non-nullable property will not be initialized after the constructor has executed. This is a problem for models that are expected to be initialized by e.g. data binding, mapping, or deserialization.

We used to work around this using the `[NotNull, DisallowNull]` attributes on a nullable property, which I liked as it was explicit about what it was doing. Unfortunately, as of .NET 5.0.4 (SDK 5.0.201), that now throws a `CS8616` as well. Given that, we need to instead use the less obvious null-forgiving operator instead with these cases.

Given this, I've replaced the cases where we were using `[NotNull, DisallowNull]` with `= default!;` on a non-nullable type instead.

Author: JeremyCaney

OnTopic.Editor.AspNetCore.Attributes/FileListAttribute/FileListAttributeViewModel.cs

@@ -62,8 +62,8 @@ public FileListAttributeViewModel(
     ///   While the <i>relative</i> file path can be retrieved from <see cref="FileListAttributeDescriptorViewModel.Path"
     ///   />, that doesn't include the base path of the web application. The <see cref="AbsolutePath"/> addresses this.
     /// </remarks>
-    [Required, NotNull, DisallowNull]
-    public string? AbsolutePath { get; set; }
+    [Required]
+    public string AbsolutePath { get; set; } = default!;
 
   } // Class
 } // Namespace

OnTopic.Editor.AspNetCore/Models/AttributeBindingModel.cs

@@ -43,35 +43,23 @@ public AttributeBindingModel(string editorType) {
     /// <summary>
     ///   The unique name associated with the specified attribute.
     /// </summary>
-    [NotNull, DisallowNull]
-    public string? Key {
-      get;
-      init;
-    }
+    public string Key { get; init; } = default!;
 
     /*==========================================================================================================================
     | EDITOR TYPE
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <summary>
     ///   The editor type associated with the attribute.
     /// </summary>
-    [NotNull, DisallowNull]
-    public string? EditorType {
-      get;
-      init;
-    }
+    public string EditorType { get; init; } = default!;
 
     /*==========================================================================================================================
     | VALUE
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <summary>
     ///   The value associated with the attribute.
     /// </summary>
-    [NotNull, DisallowNull]
-    public string? Value {
-      get;
-      init;
-    }
+    public string Value { get; init; } = default!;
 
     /*==========================================================================================================================
     | GET VALUE

OnTopic.Editor.AspNetCore/Models/ClientResources/ClientResource.cs

@@ -22,8 +22,7 @@ public abstract class ClientResource {
     /// <summary>
     ///   Gets or sets the URL associated with the client-side resource.
     /// </summary>
-    [NotNull, DisallowNull]
-    public Uri? Url { get; set; }
+    public Uri Url { get; set; } = default!;
 
   }
 }

OnTopic.Editor.AspNetCore/Models/EditorViewModel.cs

@@ -23,8 +23,7 @@ public record EditorViewModel {
     ///   The <see cref="EditingTopicViewModel"/> representing the core properties of the currently selected <see
     ///   cref="Topic"/>.
     /// </summary>
-    [NotNull, DisallowNull]
-    public EditingTopicViewModel? Topic { get; init; }
+    public EditingTopicViewModel? Topic { get; init; } = default!;
 
     /*==========================================================================================================================
     | CONTENT TYPE DESCRIPTOR
@@ -33,8 +32,7 @@ public record EditorViewModel {
     ///   The <see cref="ContentTypeDescriptorViewModel"/> representing the core properties of the <see cref="Topic"/>'s <see
     ///   cref="ContentTypeDescriptor"/>.
     /// </summary>
-    [NotNull, DisallowNull]
-    public ContentTypeDescriptorViewModel? ContentTypeDescriptor { get; init; }
+    public ContentTypeDescriptorViewModel ContentTypeDescriptor { get; init; } = default!;
 
     /*==========================================================================================================================
     | IS MODAL?

OnTopic.Editor.AspNetCore/Models/Metadata/AttributeDescriptorViewModel.cs

@@ -64,17 +64,17 @@ public record AttributeDescriptorViewModel: CoreTopicViewModel {
     ///   The <see cref="EditorType"/> corresponds to the <see cref="AttributeDescriptor"/> subtype name, such as <c>
     ///   BooleanAttributeDescriptor</c>. This can be used by the editor to determine the appropriate view component to display.
     /// </remarks>
-    [Required, NotNull, DisallowNull]
-    public string? EditorType { get; init; }
+    [Required]
+    public string EditorType { get; init; } = default!;
 
     /*==========================================================================================================================
     | PROPERTY: DISPLAY GROUP
     \-------------------------------------------------------------------------------------------------------------------------*/
     /// <summary>
     ///   Determines what group of attributes to associate the current attribute with.
     /// </summary>
-    [Required, NotNull, DisallowNull]
-    public string? DisplayGroup { get; init; }
+    [Required]
+    public string DisplayGroup { get; init; } = default!;
 
     /*==========================================================================================================================
     | PROPERTY: IS REQUIRED?