handling empty fields (no data)
Currently, if a {placeholder} doesn't get data from populating, it says "undefined".

Would be great if his could be configured – a string (or strings) that could be used instead of "undefined" (not sure how and which granularity).

But also, imagine having {price} and {oldprice}. Some data rows don't have "oldprice" though because there's no price change to communicate. In this case it would be good if a placeholder could be omitted.

I'm not all clear how we could do this. Flag a {placeholder} as optional somehow? 
