I do not know how to reproduce this (and didn't bother to look deeply into it after I found it was not a trivial fix) but one of my "git fetch" showed
warning: Submodule in commit be2db96a6c506464525f588da59cade0cedddb5e at path: '(null)' collides with a submodule named the same. Skipping it. I think it's reported that some libc implementation will not be able to gracefully handle NULL strings like glibc and may crash instead of printing '(null)' here. I'll leave it to submodule people to fix this :) -- Duy
