code: private void deleteHistoryReference() {
  		if (reference == null) {
  			return;
  		}
  
  		if (getExtensionHistory() != null) {
  			getExtensionHistory().delete(reference);
  			reference = null;
  		}
  	}
docs: Deletes the history reference, should be called when no longer needed.
  <p>
  The call to this method has no effect if the history reference no longer exists (i.e. {@code null}).
  
  @see #reference