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.COLLECTION;
				co = (Collection) oContent;
			}
			else if ( oContent instanceof String[] )
			{
				iContentType = IConstants.NON_PRIMITIVE_ARRAY;
				sa = (String[]) oContent;
			}
		}
		else
		{
			
			if ( oContent instanceof Collection )
			{
				iContentType = IConstants.COLLECTION;
				co = (Collection) oContent;
			}
			else if ( oContent instanceof Object[] )
			{
				iContentType = IConstants.NON_PRIMITIVE_ARRAY;
				oa = (Object[]) oContent;
			}
			iDataType = IConstants.UNDEFINED;
		}
		if ( iContentType == IConstants.UNDEFINED )
		{
			throw new IllegalArgumentException( MessageFormat.format( Messages.getResourceBundle( )
					.getString( "exception.process.content.type" ), 
					new Object[]{