Upgrade 2.0.15 > 2.1 rc 2 is_writable() error

[Dominus Arbitrationis]

I just updated my test forum (A complete copy of my normal forum, database, files, everything), and it appears to work without issue. However, it does blow up the error log, saying "2: is_writable() expects parameter 1 to be a valid path, array given". A screenshot has been attached. No other issues are noted, and no errors reported during upgrade process, all files and directories are owned by the normal user/group (Our webserver account, essentially, which should allow it to edit as needed)

EDIT: Added screenshot to main post.

[d3vcho]

Sorry, there's no screenshot attached.

[Dominus Arbitrationis]

Crap, sorry about that. Thank you for letting me know!

[albertlast]

related fix https://github.com/SimpleMachines/SMF2.1/pull/5716