Problem Definition

REST API: Internal Server Error (500) setting custom fields to null on create request

Call: https://INSTANCE.atlassian.net/rest/servicedeskapi/latest/request

{
    "serviceDeskId": "1",
    "requestTypeId": "2",
    "requestFieldValues": \{
        "summary": "Request JSD help via REST",
        "description": "I need a new mouse for my Mac",
      "customfield_10106":null
    }
}

Suggested Solution

The rest should accept the null entry or behave the same as if the field had nothing set.

Workaround

Leave the custom field empty ("customfield_10106":"") OR do not add it.