If HEAD of a repository points to a conflict reference, such as:
* There exist a reference named 'refs/heads/jx/feature1', but HEAD
points to 'refs/heads/jx', or
* There exist a reference named 'refs/heads/feature', but HEAD points
to 'refs/heads/feature/bad'.
When we push to delete a reference for this repo, such as:
git push /path/to/bad-head-repo.git :some/good/reference
The git-receive-pack process will crash.
This is because if HEAD points to a conflict reference, the function
`resolve_refdup("HEAD", ...)` does not return a valid reference name,
but a null buffer. Later matching the delete reference against the null
buffer will cause git-receive-pack crash.
Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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