Yeah, so even if you turn off basic authentication and specify a different auth method, Apache (at least some versions of it) still looks around for an auth file and throws a “pcfg_openfile() called with NULL” error when it can’t find one.  To fix, set the user auth file to /dev/null:

AuthBasicAurhorative off
AuthUserFile /dev/null


Or you can just ignore the errror I suppose. It looks more serious than it is.