I've tried a few things suggested, but nothing seems to remove it. This started occurring when I upgraded to Mountain Lion OS X. Anytime I do a git pull, it displays this annoying as heck empty editor with the title MERGE_MSG.
How do I prevent that from popping up globally across all my apps?
You can either pass --no-edit to git pull, or you can set the environment variable GIT_MERGE_AUTOEDIT to no.
From the git pull documentation:
--edit, --no-edit
Invoke an editor before committing successful mechanical merge to
further edit the auto-generated merge message, so that the user can
explain and justify the merge. The --no-edit option can be used to
accept the auto-generated message (this is generally discouraged).
The --edit option is still useful if you are giving a draft message
with the -m option from the command line and want to edit it in the
editor.
Older scripts may depend on the historical behaviour of not
allowing the user to edit the merge log message. They will see an
editor opened when they run git merge. To make it easier to adjust
such scripts to the updated behaviour, the environment variable
GIT_MERGE_AUTOEDIT can be set to no at the beginning of them.