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
DEUtil.getDisplayLabel( handle, false ),
						ReportPlatformUIImages.getImage( handle ),
						DEUtil.getExpression( handle ),
						( (ParameterHandle) handle ).getHelpText( ),
						true );
			}
			else if ( handle instanceof ParameterGroupHandle )
			{
				TreeItem groupItem = createSubTreeItem( topItem,
						DEUtil.getDisplayLabel( handle, false ),
						ReportPlatformUIImages.getImage( handle ),
						true );
				for ( Iterator itor = ( (ParameterGroupHandle) handle ).getParameters( )
						.iterator( ); itor.hasNext( ); )
				{
					ParameterHandle parameter = (ParameterHandle) itor.next( );
					createSubTreeItem( groupItem,
							parameter.getDisplayLabel( ),
							ReportPlatformUIImages.getImage( handle ),
							DEUtil.getExpression( parameter ),
							parameter.getDisplayLabel( ),
							true );
				}
			}
		}
	}
	/**
	 * Create data sets band.Must set Tree before execution.
	 * 
	 */