I've been having an issue with the following error appear in the prompt after upgrading to Yosemite. The solution was to source the git bash completion and prompt files from a local copy.
curl -o ~/.git-completion.bash https://raw.githubusercontent.com/git/git/master/contrib/completion/git-completion.bash
curl -o ~/.git-prompt.sh https://raw.githubusercontent.com/git/git/master/contrib/completion/git-prompt.sh
Then in:
vi ~/bash_profile
Add:
source ~/.git-completion.bash
source ~/.git-prompt.sh
Reload terminal and you should be good to go.
Thanks!