access_raw_diffs parameter not working in API

Summary

MR changes API has access_raw_diffs parameter. Setting this parameter should "Retrieve change diffs without size limitations" but it does not return diffs.

Steps to reproduce

curl "https://gitlab.com/api/v4/projects/23980155/merge_requests/3/changes?access_raw_diffs=true"

Returns,

...
...
"changes": [
    {
      "old_path": "homework02/homework_part2.ipynb",
      "new_path": "homework02/homework_part2.ipynb",
      "a_mode": "100644",
      "b_mode": "100644",
      "new_file": false,
      "renamed_file": false,
      "deleted_file": false,
      "diff": ""
    }
  ],
  "overflow": false
}

Example Project

Example MR: amit1rrr/Practical_DL!3

What is the current bug behavior?

diff field is empty in the response.

What is the expected correct behavior?

diff field above should return actual diff since we've set access_raw_diffs=true in the request.

Output of checks

This bug happens on GitLab.com

Pinging @gitlab-org/ecosystem-team based on the recommendation here.