Bug 202254 Exception is thrown when category values are null and type of X axis is set to DateTime
chart/org.eclipse.birt.chart.ui.extension/src/org/eclipse/birt/chart/ui/swt/wizard/format/axis/AbstractAxisSubtask.java
Messages.getString( "AxisYSheetImpl.Label.LabelFormat&" ), 
				popup );
		btnAxisLabel.addSelectionListener( this );
		btnAxisLabel.setEnabled( btnLabelVisible.getSelection( ) );
		
		popup = new AxisGridLinesSheet( Messages.getString( "AxisYSheetImpl.Label.Gridlines" ), 
				getContext( ),
				getAxisForProcessing( ),
				getAxisAngleType( ) );
		Button btnGridlines = createToggleButton( cmp,
				Messages.getString( "AxisYSheetImpl.Label.Gridlines&" ), 
				popup );
		btnGridlines.addSelectionListener( this );
		if ( getAxisAngleType( ) != AngleType.Z )
		{
			
			popup = new AxisMarkersSheet( Messages.getString( "AxisYSheetImpl.Label.Markers" ), 
					getContext( ),
					getAxisForProcessing( ) );
			Button btnMarkers = createToggleButton( cmp,
					Messages.getString( "AxisYSheetImpl.Label.Markers&" ), 
					popup );
			btnMarkers.addSelectionListener( this );
			
			btnMarkers.setEnabled( !ChartUIUtil.is3DType( getChart( ) ) );
		}
		
		popup = new InteractivitySheet( Messages.getString( "AbstractAxisSubtask.Label.Interactivity" ), 
				getContext( ),
				getAxisForProcessing( ).getTriggers( ),