Unable to create a gist

When attempting to share, I receive an alert with the message:

From try.purescript.org
Failed to create gist

This is caused by a failed POST:

Request URL: https://api.github.com/gists
Request Method: POST
Status Code: 422 Unprocessable Entity

The response payload:

{
  "message": "Validation Failed",
  "errors": [
    {
      "resource": "Gist",
      "code": "missing_field",
      "field": "user"
    },
    {
      "resource": "Gist",
      "code": "missing_field",
      "field": "files"
    }
  ],
  "documentation_url": "https://developer.github.com/v3/gists/#create-a-gist"
}

Start by tracing the share flow that sends the POST request to https://api.github.com/gists and compare its request with GitHub's create-a-gist documentation linked in the report. Confirm the request supplies the required user and files fields, then verify sharing no longer produces the 422 alert.