added serialzed dictionary

Packages/SerializedDictionary-main/Runtime/Scripts/SerializedCollectionsUtility.cs

@@ -0,0 +1,22 @@
+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+
+namespace AYellowpaper.SerializedCollections
+{
+    public static class SerializedCollectionsUtility
+    {
+        public static bool IsValidKey(object obj)
+        {
+            // we catch this error if we are not on the main thread and simply return false as we assume the object is null
+            try
+            {
+                return !(obj is Object unityObject && unityObject == null);
+            }
+            catch
+            {
+                return false;
+            }
+        }
+    }
+}