Comment 2 for bug 1748712

Deleting that event row allowed the upgrade to proceed:

$ sudo dpkg --configure -a
Setting up maas-region-controller (2.4.0~alpha1-6573-g12ee2331b-0ubuntu1) ...
Operations to perform:
  Apply all migrations: auth, contenttypes, maasserver, metadataserver, piston3, sessions, sites
Running migrations:
  Applying maasserver.0131_update_event_model_for_audit_logs... OK
  Applying maasserver.0132_consistent_model_name_validation... OK
  Applying maasserver.0133_add_resourcepool_model... OK
  Applying maasserver.0134_create_default_resourcepool... OK
  Applying maasserver.0135_add_pool_reference_to_node... OK
  Applying maasserver.0136_add_user_role_models... OK
  Applying maasserver.0137_create_default_roles... OK
  Applying maasserver.0138_add_ip_and_user_agent_to_event_model... OK
  Applying maasserver.0139_add_endpoint_and_increase_user_agent_length_for_event... OK
  Applying maasserver.0140_add_usergroup_model... OK
  Applying maasserver.0141_add_default_usergroup... OK
  Applying maasserver.0142_pod_default_resource_pool... OK
  Applying maasserver.0143_blockdevice_firmware... OK
  Applying maasserver.0144_filesystem_zfsroot_support... OK
  Applying metadataserver.0016_script_model_fw_update_and_hw_config... OK
  Applying metadataserver.0017_store_requested_scripts... OK
  Applying sites.0002_alter_domain_unique... OK
Setting up maas (2.4.0~alpha1-6573-g12ee2331b-0ubuntu1) ...