In the course of T152474 I identified that some emails have been created recently with blank location_type_id fields. It is not a large number and I couldn't see why are a bit of a dig.

I suggest we

1. run all the cleanups in T152474 to get back to there being none
2. do our next monthly civicm upgrade & 'get it clean again'
3. in perhaps a month bring this into the sprint & see if new ones have happened & investigate

Or else we might pick up T150388 first & get them 'clean' and them when something makes them 'not clean' that would be when we dig