Bug 147687 Assert err happened with design ui
Run BIRT in workbench with argument -ea. Assert err happened when using design ui to open a design file.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/internal/ui/dialogs/ExpressionTreeSupport.java
DesignElementHandle handle = (DesignElementHandle) currentEditObject;
			Map argMap = DEUtil.getDesignElementMethodArguments( handle,
					methodName );
			for ( Iterator iter = argMap.keySet( ).iterator( ); iter.hasNext( ); )
			{
				String argName = (String) iter.next( );
				createSubTreeItem( contextItem,
						argName,
						IMAGE_METHOD,
						argName,
						"", 
						true );
			}
		}
	}
	public void setCurrentEditObject( Object obj )
	{
		this.currentEditObject = obj;
		removeTreeItem( );
	}
	
	private void removeTreeItem( )
	{
		if ( contextItem == null || contextItem.isDisposed( ) )
			return;
		TreeItem[] items = contextItem.getItems( );
		for ( int i = 0; i < items.length; i++ )
		{
			if ( items[i] != null && !items[i].isDisposed( ) )
			{