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
{
				iContentType = IConstants.NON_PRIMITIVE_ARRAY;
				ca = (Calendar[]) oContent;
			}
			updateDateTimeValues( );
		}
		else if ( ds instanceof TextDataSet )
		{
			iDataType = IConstants.TEXT;
			if ( oContent instanceof Collection )
			{
				iContentType = IConstants.COLLECTION;
				co = (Collection) oContent;
			}
			else if ( oContent instanceof String[] )
			{
				iContentType = IConstants.NON_PRIMITIVE_ARRAY;
				sa = (String[]) oContent;
			}
		}
		else
		{
			
			iDataType = IConstants.OTHER;
			if ( oContent instanceof Collection )
			{
				iContentType = IConstants.COLLECTION;
				co = (Collection) oContent;
			}
			else if ( oContent instanceof Object[] )