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
initEReference( getSeriesDefinition_Grouping( ),
				this.getSeriesGrouping( ),
				null,
				"grouping", null, 0, 1, SeriesDefinition.class, !IS_TRANSIENT, !IS_VOLATILE, IS_CHANGEABLE, IS_COMPOSITE, !IS_RESOLVE_PROXIES, !IS_UNSETTABLE, IS_UNIQUE, !IS_DERIVED, IS_ORDERED ); 
		initEAttribute( getSeriesDefinition_Sorting( ),
				theAttributePackage.getSortOption( ),
				"sorting", "Ascending", 0, 1, SeriesDefinition.class, !IS_TRANSIENT, !IS_VOLATILE, IS_CHANGEABLE, IS_UNSETTABLE, !IS_ID, !IS_UNIQUE, !IS_DERIVED, IS_ORDERED ); 
		initEClass( seriesGroupingEClass,
				SeriesGrouping.class,
				"SeriesGrouping", !IS_ABSTRACT, !IS_INTERFACE, IS_GENERATED_INSTANCE_CLASS ); 
		initEAttribute( getSeriesGrouping_Enabled( ),
				theXMLTypePackage.getBoolean( ),
				"enabled", null, 1, 1, SeriesGrouping.class, !IS_TRANSIENT, !IS_VOLATILE, IS_CHANGEABLE, IS_UNSETTABLE, !IS_ID, !IS_UNIQUE, !IS_DERIVED, IS_ORDERED ); 
		initEAttribute( getSeriesGrouping_GroupingUnit( ),
				theAttributePackage.getGroupingUnitType( ),
				"groupingUnit", "Seconds", 1, 1, SeriesGrouping.class, !IS_TRANSIENT, !IS_VOLATILE, IS_CHANGEABLE, IS_UNSETTABLE, !IS_ID, !IS_UNIQUE, !IS_DERIVED, IS_ORDERED ); 
		initEReference( getSeriesGrouping_GroupingOrigin( ),
				this.getDataElement( ),
				null,
				"groupingOrigin", null, 1, 1, SeriesGrouping.class, !IS_TRANSIENT, !IS_VOLATILE, IS_CHANGEABLE, IS_COMPOSITE, !IS_RESOLVE_PROXIES, !IS_UNSETTABLE, IS_UNIQUE, !IS_DERIVED, IS_ORDERED ); 
		initEAttribute( getSeriesGrouping_GroupingInterval( ),
				theXMLTypePackage.getInt( ),
				"groupingInterval", null, 1, 1, SeriesGrouping.class, !IS_TRANSIENT, !IS_VOLATILE, IS_CHANGEABLE, IS_UNSETTABLE, !IS_ID, !IS_UNIQUE, !IS_DERIVED, IS_ORDERED ); 
		initEAttribute( getSeriesGrouping_GroupType( ),
				theAttributePackage.getDataType( ),
				"groupType", "Numeric", 1, 1, SeriesGrouping.class, !IS_TRANSIENT, !IS_VOLATILE, IS_CHANGEABLE, IS_UNSETTABLE, !IS_ID, !IS_UNIQUE, !IS_DERIVED, IS_ORDERED ); 
		initEAttribute( getSeriesGrouping_AggregateExpression( ),
				theXMLTypePackage.getString( ),
				"aggregateExpression", null, 1, 1, SeriesGrouping.class, !IS_TRANSIENT, !IS_VOLATILE, IS_CHANGEABLE, !IS_UNSETTABLE, !IS_ID, !IS_UNIQUE, !IS_DERIVED, IS_ORDERED ); 
		initEClass( stockDataSetEClass,