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
return ca.length;
			}
		}
		else if ( iDataType == IConstants.TEXT )
		{
			return sa.length;
		}
		else if ( oa != null )
		{
			return oa.length;
		}
		return -1; 
	}
	/**
	 * @return
	 */
	public final double nextPrimitiveDouble( )
	{
		return da[iCursor++];
	}
	/**
	 * @return
	 */
	public final Double nextDouble( )
	{
		if ( it != null )
		{
			iCursor++;
			return (Double) it.next( );
		}