Bug 152430 Key can modify to empty string
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/command/PropertyCommand.java
PropertyValueException.DESIGN_EXCEPTION_ITEM_NOT_FOUND );
		doRemoveItem( prop, posn, value );
	}
	/**
	 * Removes structure from structure list.
	 * 
	 * @param structRef
	 *            reference to the item to remove
	 */
	private void doRemoveItem( ElementPropertyDefn prop, int posn, Object item )
	{
		String label = ModelMessages
				.getMessage( MessageConstants.REMOVE_ITEM_MESSAGE );
		ActivityStack stack = module.getActivityStack( );
		stack.startTrans( label );
		makeLocalCompositeValue( prop );
		List list = element.getListProperty( module, prop.getName( ) );
		assert list != null;
		SimplePropertyListRecord record = new SimplePropertyListRecord(
				element, prop, list, posn );
		stack.execute( record );
		if ( item instanceof ElementRefValue )
		{
			ElementRefValue refValue = (ElementRefValue) item;
			if ( refValue.isResolved( ) )
			{
				ElementRefRecord refRecord = new ElementRefRecord( element,
						refValue.getTargetElement( ), prop.getName( ), false );
				stack.execute( refRecord );
			}