In the rename collection coordinator, the target collection's UUID is set on the coordinator document before the critical section is taken for that namespace. This allows for a case in which the UUID is set as none (collection doesn't exist) and then a createCollection happens just before the critical section is acquired since create does not always acquire the DDL lock.

Though this is a bug, it seems to not actually manifest in any problematic way, since the rename participant handles this situation gracefully. However, it is a potential footgun for the future which could be fixed simply by setting the uuid a few lines lower once the critical section is acquired.