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
{
		DifferenceDataSetImpl differenceDataSet = new DifferenceDataSetImpl( );
		return differenceDataSet;
	}
	/**
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	public GanttDataSet createGanttDataSet( )
	{
		GanttDataSetImpl ganttDataSet = new GanttDataSetImpl( );
		return ganttDataSet;
	}
	/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	public NumberDataElement createNumberDataElement( )
	{
		NumberDataElementImpl numberDataElement = new NumberDataElementImpl( );
		return numberDataElement;
	}
	/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	public NumberDataSet createNumberDataSet( )
	{
		NumberDataSetImpl numberDataSet = new NumberDataSetImpl( );