diff --git a/.github/workflows/package.yaml b/.github/workflows/package.yaml
index f0238d2..5284801 100644
--- a/.github/workflows/package.yaml
+++ b/.github/workflows/package.yaml
@@ -28,9 +28,13 @@ jobs:
 
       # Build
       - name: Build .unitypackage
-        uses: game-ci/unity-builder@v2
+        uses: game-ci/unity-builder@v4
+        env:
+          UNITY_LICENSE: ${{ secrets.UNITY_LICENSE }}
+          UNITY_EMAIL: ${{ secrets.UNITY_EMAIL }}
+          UNITY_PASSWORD: ${{ secrets.UNITY_PASSWORD }}
         with:
-          unityVersion: 2020.3.8f1
+          unityVersion: 2021.3.29f1
           buildMethod: MackySoft.PackageTools.Editor.UnityPackageExporter.Export
 
       # Upload
diff --git a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/ManagedReferenceUtility.cs b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/ManagedReferenceUtility.cs
index bec2c47..5cc7223 100644
--- a/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/ManagedReferenceUtility.cs
+++ b/Assets/MackySoft/MackySoft.SerializeReferenceExtensions/Editor/ManagedReferenceUtility.cs
@@ -2,14 +2,27 @@
 using System;
 using System.Reflection;
 using UnityEditor;
+using UnityEngine;
 
 namespace MackySoft.SerializeReferenceExtensions.Editor {
 	public static class ManagedReferenceUtility {
 
 		public static object SetManagedReference (this SerializedProperty property,Type type) {
-			object obj = (type != null) ? Activator.CreateInstance(type) : null;
-			property.managedReferenceValue = obj;
-			return obj;
+			object result;
+			if (property.managedReferenceValue != null)
+			{
+				// Restore an previous values from json.
+				string json = JsonUtility.ToJson(property.managedReferenceValue);
+				result = JsonUtility.FromJson(json, type);
+			}
+			else
+			{
+				result = (type != null) ? Activator.CreateInstance(type) : null;
+			}
+			
+			property.managedReferenceValue = result;
+			return result;
+
 		}
 
 		public static Type GetType (string typeName) {