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
{
		return (DataFactory) getEFactoryInstance( );
	}
	/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	private boolean isCreated = false;
	/**
	 * Creates the meta-model objects for the package.  This method is
	 * guarded to have no affect on any invocation but its first.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	public void createPackageContents( )
	{
		if ( isCreated )
			return;
		isCreated = true;
		
		actionEClass = createEClass( ACTION );
		createEAttribute( actionEClass, ACTION__TYPE );
		createEReference( actionEClass, ACTION__VALUE );
		baseSampleDataEClass = createEClass( BASE_SAMPLE_DATA );
		createEAttribute( baseSampleDataEClass,
				BASE_SAMPLE_DATA__DATA_SET_REPRESENTATION );
		bubbleDataSetEClass = createEClass( BUBBLE_DATA_SET );
		dataElementEClass = createEClass( DATA_ELEMENT );
		dataSetEClass = createEClass( DATA_SET );