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/DataPackageImpl.java
initEClass( dateTimeDataElementEClass,
				DateTimeDataElement.class,
				"DateTimeDataElement", !IS_ABSTRACT, !IS_INTERFACE, IS_GENERATED_INSTANCE_CLASS ); 
		initEAttribute( getDateTimeDataElement_Value( ),
				theXMLTypePackage.getLong( ),
				"value", null, 1, 1, DateTimeDataElement.class, !IS_TRANSIENT, !IS_VOLATILE, IS_CHANGEABLE, IS_UNSETTABLE, !IS_ID, !IS_UNIQUE, !IS_DERIVED, IS_ORDERED ); 
		initEClass( dateTimeDataSetEClass,
				DateTimeDataSet.class,
				"DateTimeDataSet", !IS_ABSTRACT, !IS_INTERFACE, IS_GENERATED_INSTANCE_CLASS ); 
		initEClass( differenceDataSetEClass,
				DifferenceDataSet.class,
				"DifferenceDataSet", !IS_ABSTRACT, !IS_INTERFACE, IS_GENERATED_INSTANCE_CLASS ); 
		initEClass( ganttDataSetEClass,
				GanttDataSet.class,
				"GanttDataSet", !IS_ABSTRACT, !IS_INTERFACE, IS_GENERATED_INSTANCE_CLASS ); 
		initEClass( numberDataElementEClass,
				NumberDataElement.class,
				"NumberDataElement", !IS_ABSTRACT, !IS_INTERFACE, IS_GENERATED_INSTANCE_CLASS ); 
		initEAttribute( getNumberDataElement_Value( ),
				theXMLTypePackage.getDouble( ),
				"value", null, 1, 1, NumberDataElement.class, !IS_TRANSIENT, !IS_VOLATILE, IS_CHANGEABLE, IS_UNSETTABLE, !IS_ID, !IS_UNIQUE, !IS_DERIVED, IS_ORDERED ); 
		initEClass( numberDataSetEClass,
				NumberDataSet.class,
				"NumberDataSet", !IS_ABSTRACT, !IS_INTERFACE, IS_GENERATED_INSTANCE_CLASS ); 
		initEClass( orthogonalSampleDataEClass,
				OrthogonalSampleData.class,
				"OrthogonalSampleData", !IS_ABSTRACT, !IS_INTERFACE, IS_GENERATED_INSTANCE_CLASS ); 
		initEAttribute( getOrthogonalSampleData_DataSetRepresentation( ),
				theXMLTypePackage.getString( ),
				"dataSetRepresentation", null, 1, 1, OrthogonalSampleData.class, !IS_TRANSIENT, !IS_VOLATILE, IS_CHANGEABLE, !IS_UNSETTABLE, !IS_ID, !IS_UNIQUE, !IS_DERIVED, IS_ORDERED );