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/DataPackage.java
* The meta object literal for the '{@link org.eclipse.birt.chart.model.data.impl.DataElementImpl <em>Element</em>}' class.
		 * <!-- begin-user-doc -->
		 * <!-- end-user-doc -->
		 * @see org.eclipse.birt.chart.model.data.impl.DataElementImpl
		 * @see org.eclipse.birt.chart.model.data.impl.DataPackageImpl#getDataElement()
		 * @generated
		 */
		EClass DATA_ELEMENT = eINSTANCE.getDataElement( );
		/**
		 * The meta object literal for the '{@link org.eclipse.birt.chart.model.data.impl.DataSetImpl <em>Set</em>}' class.
		 * <!-- begin-user-doc -->
		 * <!-- end-user-doc -->
		 * @see org.eclipse.birt.chart.model.data.impl.DataSetImpl
		 * @see org.eclipse.birt.chart.model.data.impl.DataPackageImpl#getDataSet()
		 * @generated
		 */
		EClass DATA_SET = eINSTANCE.getDataSet( );
		/**
		 * The meta object literal for the '<em><b>Values</b></em>' attribute feature.
		 * <!-- begin-user-doc -->
		 * <!-- end-user-doc -->
		 * @generated
		 */
		EAttribute DATA_SET__VALUES = eINSTANCE.getDataSet_Values( );
		/**
		 * The meta object literal for the '{@link org.eclipse.birt.chart.model.data.impl.DateTimeDataElementImpl <em>Date Time Data Element</em>}' class.
		 * <!-- begin-user-doc -->
		 * <!-- end-user-doc -->
		 * @see org.eclipse.birt.chart.model.data.impl.DateTimeDataElementImpl
		 * @see org.eclipse.birt.chart.model.data.impl.DataPackageImpl#getDateTimeDataElement()