REST API for branches always returns `null` for `parent_ids`

Summary

When using the REST API (both v4 and v3) the field parent_ids is always null.

This seems to happen since my university instance was updated to version GitLab Community Edition 10.3.2 c375a8d. Before the update (I am not sure about the old version, but I assume it to be 10.x) the parent_ids actually contained the right data.

Steps to reproduce

Use any client or python code to GET the following URL: https://gitlab.com/api/v4/projects/13083/repository/branches https://gitlab.com/api/v3/projects/13083/repository/branches

Example Project

https://gitlab.com/api/v4/projects/13083/repository/branches

What is the current bug behavior?

The field parent_ids always has the value null

What is the expected correct behavior?

The field parent_ids should contain an array of the parent commit hashes (IDs) where this commit is depending on.

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com

Possible fixes

(If you can, link to the line of code that might be responsible for the problem)