Reproducer for the second failure (KeyError: b'null:'):
# use Bazaar for the initial checkout, though it might work with Breezy too
bzr checkout lp:libmemcached
# use Breezy for the export, with attached marks file
brz fast-export --git-branch=trunk libmemcached - --marks libmemcached-marks >/dev/null
Reproducer for the second failure (KeyError: b'null:'):
# use Bazaar for the initial checkout, though it might work with Breezy too
bzr checkout lp:libmemcached
# use Breezy for the export, with attached marks file
brz fast-export --git-branch=trunk libmemcached - --marks libmemcached-marks >/dev/null