Autocompletition fails when calling emacs with a non-existent file

When I try to open a file with emacs and that file does not exist a rather long error message gets printed when I try to do autocompletition by pressing TAB:

$ fish -v
fish, version 2.0.0
$ mkdir foo; cd foo; du
0    .
$ emacs x

...or any other character and then I press TAB for autocompletition

switch: Expected exactly one argument, got 0
/usr/local/Cellar/fishfish/OpenBeta_r2/share/fish/functions/__fish_filter_mime.fish (line 17):      switch $mime[$i]
                                                                                                               ^
in function '__fish_filter_mime',
    called on line 3 of file '/usr/local/Cellar/fishfish/OpenBeta_r2/share/fish/functions/__fish_complete_mime.fish',
    with parameter list 'text/*'

in command substitution
    called on line 11 of file '/usr/local/Cellar/fishfish/OpenBeta_r2/share/fish/functions/__fish_complete_mime.fish',

in function '__fish_complete_mime',
    called on standard input,
    with parameter list 'text/*'

in command substitution
    called on standard input,


       switch − switch ‐ conditionally execute a block of commands

switch ‐ conditionally execute a block of commands
   Synopsis
       switch VALUE; [case [WILDCARD...]; [COMMANDS...]; ...] end

switch: Type 'help switch' for related documentation

switch: Expected exactly one argument, got 0
/usr/local/Cellar/fishfish/OpenBeta_r2/share/fish/functions/__fish_filter_mime.fish (line 17):      switch $mime[$i]
                                                                                                               ^
in function '__fish_filter_mime',
    called on line 3 of file '/usr/local/Cellar/fishfish/OpenBeta_r2/share/fish/functions/__fish_complete_mime.fish',
    with parameter list 'text/*'

in command substitution
    called on line 11 of file '/usr/local/Cellar/fishfish/OpenBeta_r2/share/fish/functions/__fish_complete_mime.fish',

in function '__fish_complete_mime',
    called on standard input,
    with parameter list 'text/*'

in command substitution
    called on standard input,


       switch − switch ‐ conditionally execute a block of commands

switch ‐ conditionally execute a block of commands
   Synopsis
       switch VALUE; [case [WILDCARD...]; [COMMANDS...]; ...] end

switch: Type 'help switch' for related documentation

If the file exists, no error gets printed. If I use any other program (like "touch" for example) no error occurs. I have only observed this with emacs. I'm using version 24.2.1. As you can see in the error messages I'm on OS X and using the latest fishfish formula from brew.