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
/**
	 * Returns a new object of class '<em>Stock Data Set</em>'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return a new object of class '<em>Stock Data Set</em>'.
	 * @generated
	 */
	StockDataSet createStockDataSet( );
	/**
	 * Returns a new object of class '<em>Text Data Set</em>'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return a new object of class '<em>Text Data Set</em>'.
	 * @generated
	 */
	TextDataSet createTextDataSet( );
	/**
	 * Returns a new object of class '<em>Trigger</em>'.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return a new object of class '<em>Trigger</em>'.
	 * @generated
	 */
	Trigger createTrigger( );
	/**
	 * Returns the package supported by this factory.
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @return the package supported by this factory.
	 * @generated
	 */
	DataPackage getDataPackage( );
}