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
*/
	private final int getRowCountInternal( )
	{
		if ( iContentType == IConstants.COLLECTION )
		{
			return co.size( );
		}
		else if ( iDataType == IConstants.TEXT )
		{
			return sa.length;
		}
		else if ( iDataType == IConstants.NUMERICAL )
		{
			if ( iContentType == IConstants.PRIMITIVE_ARRAY )
			{
				return da.length;
			}
			else if ( iContentType == IConstants.NON_PRIMITIVE_ARRAY )
			{
				return dda.length;
			}
		}
		else if ( iDataType == IConstants.DATE_TIME )
		{
			if ( iContentType == IConstants.PRIMITIVE_ARRAY )
			{
				return la.length;
			}
			else if ( iContentType == IConstants.NON_PRIMITIVE_ARRAY )
			{