That doesn't seem like a good idea - IMHO you shouldn't use container_of
on NULL even if it still works in the end.

Also it might be a good idea to use more regular names: struct
ieee80211_sta *pubsta, struct sta_info *sta.

Ok.

I don't get this - that just duplicates the code above, no chance to
refactor it a bit instead of duplicating the call?

I will take a look on this first.

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Chun-Yeow