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
*/
	public static final int computeUnit( DataSetIterator dsi )
	{
		Calendar cCurr, cPrev;
		for ( int k = 0; k < iaUnitTypes.length; k++ )
		{
			cPrev = (Calendar) dsi.last( );
			dsi.reset( );
			while ( dsi.hasNext( ) )
			{
				cCurr = (Calendar) dsi.next( );
				if ( cCurr != null
						&& cPrev != null
						&& cCurr.get( iaUnitTypes[k] ) != cPrev.get( iaUnitTypes[k] ) )
				{
					return iaUnitTypes[k]; 
					
				}
				if ( cCurr != null )
				{
					cPrev = cCurr;
				}
			}
		}
		
		return Calendar.YEAR;
	}
	/**
	 * Walks through all values in a datetime array and computes the least
	 * significant unit for which a difference was noted.