relation-set does not accept json

[Stuart Bishop]

The documentation on https://juju.ubuntu.com/docs/charm.html claim that relation-set can accept json:

"Change several settings at once, with a JSON file: cat settings.json | relation-set"

This does not work, with relation-set silently failing:

root@juju-canonistack-instance-1:/var/lib/juju/units/postgresql-2/charm# echo '{"role": "bar"}' | relation-set
root@juju-canonistack-instance-1:/var/lib/juju/units/postgresql-2/charm# relation-get role $JUJU_UNIT_NAME
foo
root@juju-canonistack-instance-1:/var/lib/juju/units/postgresql-2/charm# relation-set role=bar
root@juju-canonistack-instance-1:/var/lib/juju/units/postgresql-2/charm# relation-get role $JUJU_UNIT_NAME
bar