Fix nullability warnings

UniSky.Moderation/InterpretedLabelValueDefinition.cs

@@ -106,7 +106,7 @@ public InterpretedLabelValueDefinition(LabelValueDefinition def, LabelerViewDeta
         Locales = def.Locales != null ? [.. def.Locales] : [];
     }
 
-    public LabelerViewDetailed Detailed { get; }
+    public LabelerViewDetailed? Detailed { get; }
 
     public string Identifier { get; init; }
     public LabelSeverity Severity { get; init; }

UniSky.Moderation/LabelModerationCause.cs

@@ -9,12 +9,12 @@ public LabelModerationCause() : base()
         Type = ModerationCauseType.Label;
     }
 
-    public Label Label { get; internal set; }
-    public InterpretedLabelValueDefinition LabelDef { get; internal set; }
-    public LabelTarget Target { get; internal set; }
-    public LabelPreference Setting { get; internal set; }
-    public ModerationBehavior Behavior { get; internal set; }
-    public bool NoOverride { get; internal set; }
+    public required Label Label { get; set; }
+    public required InterpretedLabelValueDefinition LabelDef { get; set; }
+    public required LabelTarget Target { get; set; }
+    public required LabelPreference Setting { get; set; }
+    public required ModerationBehavior Behavior { get; set; }
+    public required bool NoOverride { get; set; }
 
     public override string ToString()
     {

UniSky.Moderation/ModerationCause.cs

@@ -2,9 +2,9 @@
 
 public class ModerationCause
 {
-    public ModerationCauseType Type { get; internal set; }
-    public ModerationCauseSource Source { get; internal set; }
-    public byte Priority { get; internal set; }
+    public required ModerationCauseType Type { get; set; }
+    public required ModerationCauseSource Source { get; set; }
+    public required byte Priority { get; set; }
     public bool Downgraded { get; internal set; }
 
     public override string ToString()

UniSky.Moderation/ModerationCauseSource.cs

@@ -6,8 +6,8 @@ namespace UniSky.Moderation;
 public class ModerationCauseSource
 {
     public ModerationCauseSourceType Type { get; internal set; }
-    public ListViewBasic List { get; internal set; }
-    public ATDid Labeler { get; internal set; }
+    public ListViewBasic? List { get; internal set; }
+    public ATDid? Labeler { get; internal set; }
 
     public override string ToString()
     {

UniSky.Moderation/ModerationDecision.cs

@@ -356,6 +356,7 @@ public ModerationDecision AddLabel(LabelTarget target, Label label, ModerationOp
 
         this.causes.Add(new LabelModerationCause()
         {
+            Type = ModerationCauseType.Label,
             Source = isSelf || labeler == null
                 ? new ModerationCauseSource() { Type = ModerationCauseSourceType.User }
                 : new ModerationCauseSource() { Type = ModerationCauseSourceType.Labeler, Labeler = labeler.Did },

UniSky.Moderation/Polyfill/Polyfill.cs

@@ -0,0 +1,58 @@
+using System.ComponentModel;
+using System.Diagnostics.CodeAnalysis;
+
+namespace System.Runtime.CompilerServices
+{
+
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    [ExcludeFromCodeCoverage]
+    internal class IsExternalInit { }
+
+    [AttributeUsage(
+           AttributeTargets.Class |
+           AttributeTargets.Struct |
+           AttributeTargets.Field |
+           AttributeTargets.Property,
+           AllowMultiple = false,
+           Inherited = false)]
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    [ExcludeFromCodeCoverage]
+    internal sealed class RequiredMemberAttribute : Attribute { }
+
+    /// <summary>
+    /// Indicates that compiler support for a particular feature is required for the location where this attribute is applied.
+    /// </summary>
+    [AttributeUsage(AttributeTargets.All, AllowMultiple = true, Inherited = false)]
+    [ExcludeFromCodeCoverage]
+    internal sealed class CompilerFeatureRequiredAttribute : Attribute
+    {
+        /// <summary>
+        /// Creates a new instance of the <see cref="CompilerFeatureRequiredAttribute"/> type.
+        /// </summary>
+        /// <param name="featureName">The name of the feature to indicate.</param>
+        public CompilerFeatureRequiredAttribute(string featureName)
+        {
+            FeatureName = featureName;
+        }
+
+        /// <summary>
+        /// The name of the compiler feature.
+        /// </summary>
+        public string FeatureName { get; }
+
+        /// <summary>
+        /// If true, the compiler can choose to allow access to the location where this attribute is applied if it does not understand <see cref="FeatureName"/>.
+        /// </summary>
+        public bool IsOptional { get; set; }
+
+        /// <summary>
+        /// The <see cref="FeatureName"/> used for the ref structs C# feature.
+        /// </summary>
+        public const string RefStructs = nameof(RefStructs);
+
+        /// <summary>
+        /// The <see cref="FeatureName"/> used for the required members C# feature.
+        /// </summary>
+        public const string RequiredMembers = nameof(RequiredMembers);
+    }
+}