[bug] null values are not interpreted as "empty" by the cell label rendering.

[aadrian]

Hi,

'null' values are not interpreted as "empty" cells by the rendering.
Using:

        cellLabel : {
            empty: "No data on {date}",
            filled: "{count} {name} {connector} {date}"
    }

doesn't seem to apply the "empty" property on those cells.
Please see here: http://jsfiddle.net/aadrian/4aDdJ/6/
The tooltip for 9 Aug displays "0 item ..." whereas that for 10 Aug it displays correctly "No data on .."

Thanks in advance.