upgrade-charm from rev 262 to 263 fails with TypeError: execv() arg 2 must contain only strings

The diff between 262 and 263 is the commit fc2aaccfb601bc488db48b036cb6f34c19195f73 according to:
https://api.jujucharms.com/charmstore/v5/percona-cluster-263/archive/repo-info

https://github.com/openstack/charm-percona-cluster/commit/fc2aaccfb601bc488db48b036cb6f34c19195f73

How to reproduce with xenial:

$ juju deploy cs:percona-cluster-262

$ juju upgrade-charm percona-cluster
Added charm "cs:percona-cluster-263" to the model.

$ juju status
Model Controller Cloud/Region Version SLA
pxc-previous localhost-localhost localhost/localhost 2.4-beta1 unsupported

App Version Status Scale Charm Store Rev OS Notes
percona-cluster 5.6.37-26.21 error 1 percona-cluster jujucharms 263 ubuntu

Unit Workload Agent Machine Public address Ports Message
percona-cluster/0* error idle 0 10.0.8.177 3306/tcp hook failed: "upgrade-charm"

Machine State DNS Inst id Series AZ Message0 started 10.0.8.177 juju-2d9a42-0 xenial Running

Relation provider Requirer Interface Type Message
percona-cluster:cluster percona-cluster:cluster percona-cluster peer

unit-percona-cluster-0: 16:41:58 DEBUG unit.percona-cluster/0.juju-log Hardening function 'install'
unit-percona-cluster-0: 16:41:58 DEBUG unit.percona-cluster/0.juju-log Hardening function 'upgrade'
unit-percona-cluster-0: 16:41:58 DEBUG unit.percona-cluster/0.juju-log Hardening function 'config_changed'
unit-percona-cluster-0: 16:41:58 DEBUG unit.percona-cluster/0.juju-log Hardening function 'update_status'
unit-percona-cluster-0: 16:41:58 DEBUG unit.percona-cluster/0.juju-log No hardening applied to 'upgrade'
unit-percona-cluster-0: 16:41:59 DEBUG unit.percona-cluster/0.juju-log Opening db connection for root@localhost
unit-percona-cluster-0: 16:41:59 DEBUG unit.percona-cluster/0.upgrade-charm /var/lib/juju/agents/unit-percona-cluster-0/charm/hooks/charmhelpers/contrib/database/mysql.py:162: Warning: MySQL is started in --skip-name-resolve mode; you must restart it without this switch for this grant to work
unit-percona-cluster-0: 16:41:59 DEBUG unit.percona-cluster/0.upgrade-charm cursor.execute(sql)
unit-percona-cluster-0: 16:41:59 DEBUG unit.percona-cluster/0.juju-log Opening db connection for root@localhost
unit-percona-cluster-0: 16:41:59 DEBUG unit.percona-cluster/0.juju-log Opening db connection for root@localhost
unit-percona-cluster-0: 16:41:59 DEBUG unit.percona-cluster/0.juju-log Notifying peers that percona is bootstrapped (uuid=23714f30-4925-11e8-996f-b689c8455021)
unit-percona-cluster-0: 16:41:59 DEBUG unit.percona-cluster/0.upgrade-charm inactive
unit-percona-cluster-0: 16:41:59 WARNING unit.percona-cluster/0.juju-log min-cluster-size is not defined, race conditions may occur if this is not a single unit deployment.
unit-percona-cluster-0: 16:41:59 DEBUG unit.percona-cluster/0.upgrade-charm active
unit-percona-cluster-0: 16:41:59 INFO unit.percona-cluster/0.juju-log Unit is ready
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm Traceback (most recent call last):
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm File "/var/lib/juju/agents/unit-percona-cluster-0/charm/hooks/upgrade-charm", line 859, in <module>
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm main()
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm File "/var/lib/juju/agents/unit-percona-cluster-0/charm/hooks/upgrade-charm", line 855, in main
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm assess_status(register_configs())
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm File "/var/lib/juju/agents/unit-percona-cluster-0/charm/hooks/percona_utils.py", line 673, in assess_status
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm application_version_set(get_upstream_version(determine_packages()[0]))
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm File "/var/lib/juju/agents/unit-percona-cluster-0/charm/hooks/charmhelpers/core/hookenv.py", line 947, in application_version_set
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm subprocess.check_call(cmd)
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm File "/usr/lib/python2.7/subprocess.py", line 536, in check_call
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm retcode = call(*popenargs, **kwargs)
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm File "/usr/lib/python2.7/subprocess.py", line 523, in call
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm return Popen(*popenargs, **kwargs).wait()
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm File "/usr/lib/python2.7/subprocess.py", line 711, in __init__
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm errread, errwrite)
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm File "/usr/lib/python2.7/subprocess.py", line 1343, in _execute_child
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm raise child_exception
unit-percona-cluster-0: 16:42:00 DEBUG unit.percona-cluster/0.upgrade-charm TypeError: execv() arg 2 must contain only strings
unit-percona-cluster-0: 16:42:00 ERROR juju.worker.uniter.operation hook "upgrade-charm" failed: exit status 1