It complains when I do this.

cotto@feather:/usr/src/parrot/parrot-git-m0spec @m0-spec 0 $ git pull
You asked me to pull without telling me which branch you
want to merge with, and 'branch.m0-spec.merge' in
your configuration file does not tell me, either. Please
specify which branch you want to use on the command line and
try again (e.g. 'git pull <repository> <refspec>').
See git-pull(1) for details.

If you often merge with the same branch, you may want to
use something like the following in your configuration file:

    [branch "m0-spec"]
    remote = <nickname>
    merge = <remote-ref>

    [remote "<nickname>"]
    url = <url>
    fetch = <refspec>

See git-config(1) for details.