format-patch and submodules

(Seen in git versions: 2.1.0 and 1.9.3 et al.)

$ git format-patch --stdout X^..X | git apply check - fatal: unrecognized input

This fails when the commit consists of nothing but a submodule change (as in 'git add submodule foo'), but it passes when a file change is added to the same commit.

There used to be a similar problem for empty commits, but that was fixed around git-1.8:

    http://stackoverflow.com/questions/20775132/cannot-apply-git-patch-replacing-a-file-with-a-link

Now, 'git format-patch' outputs nothing for an empty commit. I suppose that needs to be the behavior also when only submodules are changed, since in that case there is no 'diff' section from 'format-patch'.

Use-case: git-p4

Of course, we do not plan to add the submodule into Perforce, but we would like this particular command to behave the same whether there are other diffs or not.

~Christopher Dunn (cdunn2001)