After installing some applications, I found that
man no longer worked on my computer:
$ man gcc No manual entry for gcc See 'man 7 undocumented' for help when manual pages are not available.
Turns out that one of the applications needed to add its manpage. It did this by adding its path to
MANPATH like this in Fish's
set --export MANPATH $MANPATH /path/to/app
Changing it to the below fixed the error:
set --export MANPATH ":/path/to/app"