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
DataSet dataSet = (DataSet) theEObject;
				Object result = caseDataSet( dataSet );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case DataPackage.DATE_TIME_DATA_ELEMENT :
			{
				DateTimeDataElement dateTimeDataElement = (DateTimeDataElement) theEObject;
				Object result = caseDateTimeDataElement( dateTimeDataElement );
				if ( result == null )
					result = caseDataElement( dateTimeDataElement );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case DataPackage.DATE_TIME_DATA_SET :
			{
				DateTimeDataSet dateTimeDataSet = (DateTimeDataSet) theEObject;
				Object result = caseDateTimeDataSet( dateTimeDataSet );
				if ( result == null )
					result = caseDataSet( dateTimeDataSet );
				if ( result == null )
					result = defaultCase( theEObject );
				return result;
			}
			case DataPackage.DIFFERENCE_DATA_SET :
			{
				DifferenceDataSet differenceDataSet = (DifferenceDataSet) theEObject;
				Object result = caseDifferenceDataSet( differenceDataSet );