Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/PropertyCommand.java
* @param item
	 *            the item to add to the list
	 * @throws SemanticException
	 *             if the item to add is invalid.
	 */
	public void addItem( ElementPropertyDefn prop, Object item )
			throws SemanticException
	{
		assert prop != null;
		if ( item == null )
			return;
		
		assert !( item instanceof IStructure );
		assertExtendedElement( module, element, prop );
		
		checkListProperty( prop );
		Object value = checkItem( prop, item );
		
		
		List list = element.getListProperty( module, prop.getName( ) );
		element.checkSimpleList( module, prop, list, value );
		ActivityStack stack = getActivityStack( );
		stack.startTrans( ModelMessages
				.getMessage( MessageConstants.ADD_ITEM_MESSAGE ) );
		makeLocalCompositeValue( prop );
		list = element.getListProperty( module, prop.getName( ) );
		if ( null == list )
		{
			list = new ArrayList( );
			PropertyRecord propRecord = new PropertyRecord( element, prop, list );