Timestamp of zero in reflog considered invalid

Hi all,

I found this issue through a test suite for a Python git interface, which during the tests at some point sets

GIT_COMMITTER_DATE=1970-01-01T00:00:00

To reproduce the issue:

$ git init $ echo foo > testfile $ git add testfile $ git commit -m "test" $ echo bar >> testfile $ export GIT_COMMITTER_DATE=1970-01-01T00:00:00 $ git stash save $ git stash apply refs/stash@{0} is not a valid reference

At this point one can see:

$ git rev-parse --symbolic --verify 'refs/stash@{0}' fatal: Log for refs/stash is empty.

Expected:

$ git rev-parse --symbolic --verify 'refs/stash@{0}' refs/stash@{0}

I tracked the issue to refs/files-backend.c in show_one_reflog_ent :

https://github.com/git/git/blob/11529ecec914d2f0d7575e6d443c2d5a6ff75424/refs/files-backend.c#L2923

in which

!(timestamp = strtoul(email_end + 2, &message, 10)) ||

implies an invalid reflog entry. Why should 0 be treated as an invalid timestamp (even if it's unlikely outside of corner cases)?

Thanks, Erik