From c21cce34b1db1292a979360bda43c82685c955a1 Mon Sep 17 00:00:00 2001
From: Mikhail <99481254+DCFApixels@users.noreply.github.com>
Date: Mon, 20 Apr 2026 20:40:46 +0800
Subject: [PATCH] fix

---
 src/Internal/Editor/DragonGUI.cs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/Internal/Editor/DragonGUI.cs b/src/Internal/Editor/DragonGUI.cs
index dd321cc..e7be718 100644
--- a/src/Internal/Editor/DragonGUI.cs
+++ b/src/Internal/Editor/DragonGUI.cs
@@ -904,7 +904,11 @@ namespace DCFApixels.DragonECS.Unity.Editors
         }
         internal static bool IsNullManagedReference(this SerializedProperty property)
         {
+#if UNITY_2021_3_OR_NEWER
             return property.managedReferenceId == ManagedReferenceUtility.RefIdNull;
+#else
+            return property.managedReferenceId == SerializationUtility.RefIdNull;
+#endif
         }
         internal static int GetChildPropertiesCount(this SerializedProperty property, Type type, out bool isEmpty)
         {