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/impl/DataFactoryImpl.java
case DataPackage.QUERY :
				return createQuery( );
			case DataPackage.RULE :
				return createRule( );
			case DataPackage.SAMPLE_DATA :
				return createSampleData( );
			case DataPackage.SERIES_DEFINITION :
				return createSeriesDefinition( );
			case DataPackage.SERIES_GROUPING :
				return createSeriesGrouping( );
			case DataPackage.STOCK_DATA_SET :
				return createStockDataSet( );
			case DataPackage.TEXT_DATA_SET :
				return createTextDataSet( );
			case DataPackage.TRIGGER :
				return createTrigger( );
			default :
				throw new IllegalArgumentException( "The class '" + eClass.getName( ) + "' is not a valid classifier" ); 
		}
	}
	/**
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	public Object createFromString( EDataType eDataType, String initialValue )
	{
		switch ( eDataType.getClassifierID( ) )
		{
			case DataPackage.DATA :