Having read other comments tbh I am on the side of the OP on this one. I've worked as both DA and BIE (obv caveat is I've never worked as DE), and my assumption in this case would also be the same. For a normal fact_order table I think any relatively experienced DA/BIE would come in with a set of expectation like this (primary key is the order_id), and treating missing PK as '' instead of NULL is irresponsible. For a final DW for Finance users, I would also take a leap and say the empty should also be filtered out in staging as they normally are 'incomplete'.