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
/**
	 * Complete the initialization of the package and its meta-model. This
	 * method is guarded to have no affect on any invocation but its first. <!--
	 * begin-user-doc --> <!-- end-user-doc -->
	 * 
	 * @generated
	 */
	public void initializePackageContents( )
	{
		if ( isInitialized )
			return;
		isInitialized = true;
		
		setName( eNAME );
		setNsPrefix( eNS_PREFIX );
		setNsURI( eNS_URI );
		
		AttributePackage theAttributePackage = (AttributePackage) EPackage.Registry.INSTANCE.getEPackage( AttributePackage.eNS_URI );
		XMLTypePackage theXMLTypePackage = (XMLTypePackage) EPackage.Registry.INSTANCE.getEPackage( XMLTypePackage.eNS_URI );
		ComponentPackage theComponentPackage = (ComponentPackage) EPackage.Registry.INSTANCE.getEPackage( ComponentPackage.eNS_URI );
		
		bubbleDataSetEClass.getESuperTypes( ).add( this.getDataSet( ) );
		dateTimeDataElementEClass.getESuperTypes( )
				.add( this.getDataElement( ) );
		dateTimeDataSetEClass.getESuperTypes( ).add( this.getDataSet( ) );
		differenceDataSetEClass.getESuperTypes( ).add( this.getDataSet( ) );
		ganttDataSetEClass.getESuperTypes( ).add( this.getDataSet( ) );
		numberDataElementEClass.getESuperTypes( ).add( this.getDataElement( ) );
		numberDataSetEClass.getESuperTypes( ).add( this.getDataSet( ) );
		stockDataSetEClass.getESuperTypes( ).add( this.getDataSet( ) );