Bug 161219 Gantt chart with null datapoints fail to render
Create a dataset with two date columns, having some null date values Create a gantt chart Assign the dates to the gant series It fails to render and throw exception. Expected: null dates should be treated as: - 1 null date, 1 valid date ->one marker drawn, no line - 2 null dates -> skip rendering of datapoint If the decoration label is missing it should also not fail.
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/util/CDateTime.java
* @return The hour associated with this instance
	 */
	public final int getHour( )
	{
		return get( Calendar.HOUR_OF_DAY );
	}
	/**
	 * Returns the minute associated with this instance
	 * 
	 * @return The minute associated with this instance
	 */
	public final int getMinute( )
	{
		return get( Calendar.MINUTE );
	}
	/**
	 * Returns the second associated with this instance
	 * 
	 * @return The second associated with this instance
	 */
	public final int getSecond( )
	{
		return get( Calendar.SECOND );
	}
	/**
	 * Returns the most significant datetime unit in which there's a difference
	 * or 0 if there is no difference.
	 * 
	 * @return The least significant 'Calendar' unit in which a difference
	 *         occurred