Having fun with NaNs and mixed units in matrices

I had matrices with mixed unit and NaNs in calculation and kept getting units errors. It was a surprise to me that NaN would grab the unit from the first matrix element. After realizing that I found a similar thread about same happening with 0 values. In that case it was solved with zero. Interestingly that doesn't show in the list of units and I couldn't find it in the help either.

Anyway, for my purposes to solutions seems possible: either moving the unit row to bottom or to utilize zero with the NaN:

There's no question here, but I do find the behaviour more than a little odd...