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/computation/DataSetIterator.java
it = null;
	}
	/**
	 * 
	 */
	public final void notifyDataUpdate( )
	{
		reset( );
		iRowCount = getRowCountInternal( );
	}
	/**
	 * 
	 */
	final void updateDateTimeValues( ) throws ChartException
	{
		iRowCount = getRowCountInternal( );
		Calendar cValue;
		CDateTime[] cdta = new CDateTime[size( )];
		reset( );
		int i = 0;
		while ( hasNext( ) )
		{
			cValue = (Calendar) next( );
			cdta[i++] = ( cValue == null ) ? null : new CDateTime( cValue );
		}