While I found similar question I didn't find an answer to my problem

When I try to rename the directory from FOO to foo via git mv FOO foo I get

fatal: renaming 'FOO' failed: Invalid argument

OK. So I try git mv FOO foo2 && git mv foo2 foo

But when I try to commit via git commit . I get

# On branch master
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
# foo
nothing added to commit but untracked files present (use "git add" to track)

When I add the directory via git add foo nothing changes and git commit . gives me the same message again.

What am I doing wrong? I thought I'm using a case-sensitive system (OSX) why can't I simply rename the directory?