Possible BUG in 'git config'

bash-3.1$ cat ./.git/config
[i18n]
        commitencoding = UTF-8

bash-3.1$ git repo-config --global user.name marco

bash-3.1$ git repo-config user.name marco

I would expect git repo-config user.name returns an empty string, because user.name is defined _only_ in global config file ~/.gitconfig

--global::
	Use global ~/.gitconfig file rather than the repository .git/config.

How it is possible to know if a variable is stored in local config file?

Thanks Marco