Yes, this need a little explanation. This is useful for Date columns. If they have their `datetime` attribute set to `True`, we will want to upload both date and time. (aha, you should know that GoodData is still middle age, and we need to upload two values if we want to have the date and the time (the time of the day is in second, yuck).

Before my little surgery, the client was creating the part of the Date column in a functional way, so I made it class-based.