Alan has a point & an Article that I would used if pressed.
Which one? 250.4 refers to the EGC so that is not relevant.
The idea of all conductors in the same raceway is to address inductive heating and that is not an issue here. Electrically this is a switch loop.
If the AHJ told me to do it, I would wire nut some white wire in there to make him happy but I would still be wondering why.
