Ticket #3303: 3303.patch

_source/core/dom/domobject.js

@@ -178 +178 @@
                 var expandoNumber = this.$._cke_expando,
                         dataSlot = expandoNumber && customData[ expandoNumber ];
 
-                if ( dataSlot && dataSlot[ key ] !== undefined )
-                        return dataSlot[ key ];
-                return null;
+                return dataSlot && dataSlot[ key ];
         };
 
         domObjectProto.removeCustomData = function( key )
         {
                 var expandoNumber = this.$._cke_expando,
                         dataSlot = expandoNumber && customData[ expandoNumber ],
-                        retval = dataSlot[ key ];
+                        retval = dataSlot && dataSlot[ key ];
 
-                delete dataSlot[ key ];
+                if ( typeof retval != 'undefined' )
+                        delete dataSlot[ key ];
+
                 return retval || null;
         };