Index: /CKEditor/trunk/_source/core/dom/domobject.js
===================================================================
--- /CKEditor/trunk/_source/core/dom/domobject.js	(revision 3353)
+++ /CKEditor/trunk/_source/core/dom/domobject.js	(revision 3354)
@@ -179,7 +179,5 @@
 			dataSlot = expandoNumber && customData[ expandoNumber ];
 
-		if ( dataSlot && dataSlot[ key ] !== undefined )
-			return dataSlot[ key ];
-		return null;
+		return dataSlot && dataSlot[ key ];
 	};
 
@@ -188,7 +186,9 @@
 		var expandoNumber = this.$._cke_expando,
 			dataSlot = expandoNumber && customData[ expandoNumber ],
-			retval = dataSlot[ key ];
-
-		delete dataSlot[ key ];
+			retval = dataSlot && dataSlot[ key ];
+
+		if ( typeof retval != 'undefined' )
+			delete dataSlot[ key ];
+
 		return retval || null;
 	};