Bug 390669 [Accessibility]Press 'Tab' doesn't focus on the next report item when adding relative period aggregation.
xtab/org.eclipse.birt.report.item.crosstab.ui/src/org/eclipse/birt/report/item/crosstab/internal/ui/dialogs/CrosstabBindingDialogHelper.java
}
			dialogCanFinish( );
			this.messageLine.setText( "" ); 
			this.messageLine.setImage( null );
			if ( txtExpression != null
					&& ( txtExpression.getText( ) == null || txtExpression.getText( )
							.trim( )
							.equals( "" ) ) ) 
			{
				dialog.setCanFinish( false );
				return;
			}
			if ( isAggregate( ) )
			{
				try
				{
					IAggrFunction aggregation = DataUtil.getAggregationManager( )
							.getAggregation( getFunctionByDisplayName( cmbFunction.getText( ) ).getName( ) );
					if ( aggregation.getParameterDefn( ).length > 0 )
					{
						IParameterDefn[] parameters = aggregation.getParameterDefn( );
						for ( IParameterDefn param : parameters )
						{
							if ( !param.isOptional( ) )
							{
								String paramValue = getControlValue( paramsMap.get( param.getName( ) ) );
								if ( paramValue == null
										|| paramValue.trim( ).equals( "" ) ) 
								{
									dialog.setCanFinish( false );