Comment 7 for bug 1895954

We have a potential workaround for people impacted by this bug.

SSH to the controller machine and get access to Mongo:

agent=$(cd /var/lib/juju/agents; echo machine-*)
pw=$(sudo grep statepassword /var/lib/juju/agents/${agent}/agent.conf | cut '-d ' -sf2)

mongo --ssl -u ${agent} -p $pw --authenticationDatabase admin --sslAllowInvalidHostnames --sslAllowInvalidCertificates localhost:37017/juju

If you are in an HA controller, you will want to determine which machine is the Mongo Primary (it will have a prompt of:

juju:PRIMARY>

if you already are, and

juju:SECONDARY>

if you are not.

You can use

rs.status()

And look for the

"members": [

with "stateStr" of "PRIMARY", eg:

                        "name" : "10.5.24.54:37017",
                        "health" : 1,
                        "state" : 1,
                        "stateStr" : "PRIMARY",

From there you can run:

db.charms.find({meta: null}).count()

And see how many records should be affected. You can exit that shell and run:
mongo --ssl -u ${agent} -p $pw --authenticationDatabase admin --sslAllowInvalidHostnames --sslAllowInvalidCertificates localhost:37017/juju --eval 'db.charms.find({}).pretty()' > all_records.txt

To get a complete list of all charm records. And
mongo --ssl -u ${agent} -p $pw --authenticationDatabase admin --sslAllowInvalidHostnames --sslAllowInvalidCertificates localhost:37017/juju --eval 'db.charms.find({"meta": null}).pretty()' > null_records.txt

To get just the null records.

And then
mongo --ssl -u ${agent} -p $pw --authenticationDatabase admin --sslAllowInvalidHostnames --sslAllowInvalidCertificates localhost:37017/juju --eval 'db.charms.update({meta: null}, { $set: {"meta": {}} }, false, true)'

Which will update the records with a nil meta to one with an empty meta, avoiding the nil pointer dereference.
You should see a line like:
WriteResult({ "nMatched" : 0, "nUpserted" : 0, "nModified" : 0 })

Where the nModified matches the count() from earlier.