Bug 202254 Exception is thrown when category values are null and type of X axis is set to DateTime
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/model/data/util/DataSwitch.java
if ( result == null )
					result = caseDataSet( differenceDataSet );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case DataPackage.GANTT_DATA_SET :
			{
				GanttDataSet ganttDataSet = (GanttDataSet) theEObject;
				Object result = caseGanttDataSet( ganttDataSet );
				if ( result == null )
					result = caseDataSet( ganttDataSet );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case DataPackage.NUMBER_DATA_ELEMENT :
			{
				NumberDataElement numberDataElement = (NumberDataElement) theEObject;
				Object result = caseNumberDataElement( numberDataElement );
				if ( result == null )
					result = caseDataElement( numberDataElement );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case DataPackage.NUMBER_DATA_SET :
			{
				NumberDataSet numberDataSet = (NumberDataSet) theEObject;
				Object result = caseNumberDataSet( numberDataSet );