Use helper function to compare guid (#10825)

src/Jellyfin.Extensions/GuidExtensions.cs

@@ -0,0 +1,26 @@
+using System;
+using System.Diagnostics.CodeAnalysis;
+
+namespace Jellyfin.Extensions;
+
+/// <summary>
+/// Guid specific extensions.
+/// </summary>
+public static class GuidExtensions
+{
+    /// <summary>
+    /// Determine whether the guid is default.
+    /// </summary>
+    /// <param name="guid">The guid.</param>
+    /// <returns>Whether the guid is the default value.</returns>
+    public static bool IsEmpty(this Guid guid)
+        => guid.Equals(default);
+
+    /// <summary>
+    /// Determine whether the guid is null or default.
+    /// </summary>
+    /// <param name="guid">The guid.</param>
+    /// <returns>Whether the guid is null or the default valueF.</returns>
+    public static bool IsNullOrEmpty([NotNullWhen(false)] this Guid? guid)
+        => guid is null || guid.Value.IsEmpty();
+}

src/Jellyfin.Extensions/Json/Converters/JsonNullableGuidConverter.cs

@@ -18,7 +18,7 @@ namespace Jellyfin.Extensions.Json.Converters
         {
             // null got handled higher up the call stack
             var val = value!.Value;
-            if (val.Equals(default))
+            if (val.IsEmpty())
             {
                 writer.WriteNullValue();
             }