When pushing, git/send would sometimes decide we had all the
objects that we'd need to update the remote, and would try
to pack and send the entire history of the repository. This
is because we only set the 'theirs' ref when we had the object.
If we didn't have the object, we would set a zero hash,
then when deciding if we needed to force, we would think
that we were updating a new branch and send everything,
which would fail to update the remote.
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