Add JsonConverter for Nullable Guids

MediaBrowser.Common/Json/Converters/JsonNullableGuidConverter.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Globalization;
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace MediaBrowser.Common.Json.Converters
+{
+    /// <summary>
+    /// Converts a GUID object or value to/from JSON.
+    /// </summary>
+    public class JsonNullableGuidConverter : JsonConverter<Guid?>
+    {
+        /// <inheritdoc />
+        public override Guid? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+        {
+            var guidStr = reader.GetString();
+            return guidStr == null ? null : new Guid(guidStr);
+        }
+
+        /// <inheritdoc />
+        public override void Write(Utf8JsonWriter writer, Guid? value, JsonSerializerOptions options)
+        {
+            if (value == null || value == Guid.Empty)
+            {
+                writer.WriteNullValue();
+            }
+            else
+            {
+                writer.WriteStringValue(value.Value.ToString("N", CultureInfo.InvariantCulture));
+            }
+        }
+    }
+}