Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/PropertyCommand.java
return;
			}
		}
		PropertyRecord record = new PropertyRecord( element, prop, value );
		getActivityStack( ).execute( record );
	}
	/**
	 * Justifies whether the extended element is created if the UI invokes some
	 * operations to change the extension properties.
	 * 
	 * Note that <code>PropertyCommand</code> do not support structure
	 * operations like addItem, removeItem, etc. for extension elements. This
	 * method is kept but NERVER call it in <code>doSetProperty</code>.
	 * 
	 * @param module
	 *            the module
	 * @param element
	 *            the extended item that holds the extended element
	 * @param prop
	 *            the extension property definition to change
	 */
	private void assertExtendedElement( Module module, DesignElement element,
			PropertyDefn prop )
	{
		if ( element instanceof ExtendedItem )
		{
			if ( prop.isExtended( ) )
				assert ( (ExtendedItem) element ).getExtendedElement( ) != null;
		}
	}