DocDB: parameter group name set to null fails major version upgrade

Terraform Providers AWS
1

Attempt to upgrade:

  • DocDB 3.6 with an associated custom parameters group
    to
  • DocDB 5 with a default associated parameters group

fails with the following error:
InvalidParameterCombination: The current DB cluster parameter group ci-scimservice is custom. You must explicitly specify a new DB cluster parameter group, either default or custom, for the engine version upgrade.

I’ve hoped this:

db_cluster_parameter_group_name = null

would make it work.