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
/**
	 * 
	 * @param ds
	 * @throws UnexpectedInputException
	 */
	public DataSetIterator( Double[] dda )
	{
		this.dda = dda;
		iDataType = IConstants.NUMERICAL;
		iContentType = IConstants.NON_PRIMITIVE_ARRAY;
		iRowCount = dda.length;
	}
	/**
	 * 
	 * @param sa
	 */
	public DataSetIterator( String[] sa )
	{
		this.sa = sa;
		iDataType = IConstants.TEXT;
		iContentType = IConstants.NON_PRIMITIVE_ARRAY;
		iRowCount = sa.length;
	}
	/**
	 * 
	 * @param sa
	 */
	public DataSetIterator( Calendar[] ca ) throws ChartException
	{
		this.ca = ca;