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/DataFactory.java
*/
	DataSet createDataSet( );
	/**
	 * Returns a new object of class '<em>Date Time Data Element</em>'. <!-- begin-user-doc --> <!-- end-user-doc
	 * -->
	 * 
	 * @return a new object of class '<em>Date Time Data Element</em>'.
	 * @generated
	 */
	DateTimeDataElement createDateTimeDataElement( );
	/**
	 * Returns a new object of class '<em>Date Time Data Set</em>'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return a new object of class '<em>Date Time Data Set</em>'.
	 * @generated
	 */
	DateTimeDataSet createDateTimeDataSet( );
	/**
	 * Returns a new object of class '<em>Difference Data Set</em>'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return a new object of class '<em>Difference Data Set</em>'.
	 * @generated
	 */
	DifferenceDataSet createDifferenceDataSet( );
	/**
	 * Returns a new object of class '<em>Gantt Data Set</em>'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return a new object of class '<em>Gantt Data Set</em>'.