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
/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	public EAttribute getSeriesGrouping_GroupingInterval( )
	{
		return (EAttribute) seriesGroupingEClass.getEStructuralFeatures( )
				.get( 3 );
	}
	/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	public EAttribute getSeriesGrouping_GroupType( )
	{
		return (EAttribute) seriesGroupingEClass.getEStructuralFeatures( )
				.get( 4 );
	}
	/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated
	 */
	public EAttribute getSeriesGrouping_AggregateExpression( )
	{
		return (EAttribute) seriesGroupingEClass.getEStructuralFeatures( )
				.get( 5 );
	}
	/**
	 * <!-- begin-user-doc --> <!-- end-user-doc -->
	 * @generated