git add --intent-to-add silently creates empty commits

Hello,

I think this is an unintended behavior, but I might be wrong:

Using `git add -N` allows creating of empty commits:


git init test && cd test
echo text > file
git add --intent-to-add file
git commit -m 'Empty commit'
echo $?                                    # prints 0
git log -1 -p --format='' HEAD | wc -l     # prints 0
git status -s                              # prints `AM file`


I'd expect `git commit` to error out instead of producing an empty commit.

I've seen this with git 2.8.1 and 2.10.0.129.g35f6318

Thanks,
Aviv