Branches of private projects couldn't be accessed through API

Summary

Calling repository branches API for private project returns 404 error in Gitlab CE.

Steps to reproduce

You could easily check GET branches API for any project created as private.

What is the current bug behavior?

Calling API returns 404 error.

There is not any info about the API if it is for only public projects, hence I think this is a valid bug ;) API does work fine for public projects.

What is the expected correct behavior?

API should return also branches for private projects.