修复空引用

Assets/Unity-Tools/ExcelResolver/Editor/Core/Data/ClassCodeData.cs

@@ -24,11 +24,14 @@ namespace Tools.ExcelResolver.Editor
             fields.Clear();
             fields = null;
 
-            foreach (var fieldData in keyField)
+            if (keyField != null)
             {
-                fieldData?.Dispose();
+                foreach (var fieldData in keyField)
+                {
+                    fieldData?.Dispose();
+                }
+                keyField = null;
             }
-            keyField = null;
         }
     }
 }