code: private void updateObjectFieldsForEditor(PropertyEditor editor,
  	                                         BioPAXElement update,
  	                                         BioPAXElement existing,
  	                                         Model target)
  	{
  		if (editor.isMultipleCardinality())
  		{
  			for (Object updateValue : editor.getValueFromBean(update))
  			{
  				updateField(editor, updateValue, existing, target);
  			}
  		}
  		else
  		{
  			Set existingValue = editor.getValueFromBean(existing);
  			Set updateValue = editor.getValueFromBean(update);
  			if (editor.isUnknown(existingValue))
  			{
  				if (!editor.isUnknown(updateValue))
  				{
  					updateField(editor, updateValue.iterator().next(), existing, target);
  				}
  			}
  			else {
  				if (!existingValue.equals(updateValue))
  					log.info("Keep existing single cardinality property value: " +
  						existingValue + " (ignore: " + updateValue + ")" );
  			}
  		}
  	}
docs: Updates the value of <em>existing</em> element, using the value of <em>update</em>.
  Editor is used for the modification.
  
  @param editor   editor for the specific value to be updated
  @param update   BioPAX element of which value is used for the update
  @param existing BioPAX element to be updated
  @param target