Unified Datafeed: problems handling blank columns

Files after 2/15 for bills.com can be handled with the attached file supposedly.
However after reviewing with Patrick, it appears that the unified data feed does
not handle blank fields yet. I actually remember discussing this and it may have
been a design choice. MAY.

In any case, there are 2 parts to the problem:

1) The code cares whether any field is blank not only those it has been told to
parse from (that feels like a bug)
2) There should be a way to say if a field is blank it should be set to some
value in the xml. The value should probably be user defined. (this feels like an
enhancement and you should feel free to treat it as a product council/Ted issue)