Failed merge gets 'old_model_id' response, no error available for the user

[bronwyncombs]

Followed testing instructions from this comment

Got this error when failed in v7.9-dev

{
  "messageId": 499,
  "read": false,
  "timestamp": "2023-07-27T20:36:01",
  "type": "record-merge-failed",
  "payload": {
    "response": "local variable 'old_model_id' referenced before assignment",
    "task_id": "a759aced-be89-4c08-9393-35d888347a8a",
    "table": "Agent",
    "new_record_id": 2317,
    "old_record_ids": "[]",
    "new_record_data": "{\"id\": 2317, \"abbreviation\": null, \"agenttype\": 0, \"date1\": null, \"date1precision\": null, \"date2\": null, \"date2precision\": null, \"dateofbirth\": null, \"dateofbirthprecision\": null, \"dateofdeath\": null, \"dateofdeathprecision\": null, \"datetype\": null, \"email\": null, \"firstname\": null, \"guid\": \"ccf2da26-7f5f-4d7e-9b49-947fff423a21\", \"initials\": null, \"integer1\": null, \"integer2\": null, \"interests\": null, \"jobtitle\": null, \"lastname\": \"2\", \"middleinitial\": null, \"remarks\": null, \"suffix\": null, \"text1\": null, \"text2\": null, \"text3\": null, \"text4\": null, \"text5\": null, \"timestampcreated\": \"2023-07-27T20:27:25\", \"timestampmodified\": \"2023-07-27T20:30:44\", \"title\": null, \"url\": null, \"verbatimdate1\": null, \"verbatimdate2\": null, \"version\": 1, \"collcontentcontact\": null, \"colltechcontact\": null, \"createdbyagent\": \"/api/specify/agent/1313/\", \"division\": \"/api/specify/division/2/\", \"instcontentcontact\": null, \"insttechcontact\": null, \"modifiedbyagent\": \"/api/specify/agent/1313/\", \"organization\": null, \"specifyuser\": null, \"orgmembers\": \"/api/specify/agent/?organization=2317\", \"collectors\": \"/api/specify/collector/?agent=2317\", \"members\": \"/api/specify/groupperson/?member=2317\", \"resource_uri\": \"/api/specify/agent/2317/\", \"catalogerof\": \"/api/specify/CollectionObject?cataloger=2317\", \"addresses\": [], \"agentattachments\": [], \"agentgeographies\": [], \"agentspecialties\": [], \"variants\": [], \"groups\": []}"
  }
}

[bronwyncombs]

SELU_2_3_23: no response message for failed merge

[acwhite211]

The error "local variable 'old_model_id' referenced before assignment" seems to be do to the old_record_ids = []. I will create a PR that will catch this case.