@Override
 public void setExisting(DmcAttribute<?> attr) {
   existingValue = (DmcTypeDMPEventREFSET) attr;
   if (existingValue != null) value = existingValue.getMVCopy();
 }
 @Override
 public void resetToExisting() {
   if (existingValue == null) value = null;
   else value = existingValue.getMVCopy();
 }