Description of the problem, including code/CLI snippet

When I try to get all commits for a project and filter them by branch, I still get all commits for all branches. E.g.:

commits = project.commits.list(all=True, ref_name='master')

As far as I understand the all=True only concerns pagination and should not influence the ref_name filter, and the master branch as ref_name should be a valid input (provided that this branch exists), right?

Expected Behavior

len(commits) should be 38 and only contains commits that are on the master branch.
This was also verified using the gitlab commits overview and checking if all returned commits are indeed on master.

Actual Behavior

len(commits) is 62 and also includes commits that are on other branches that were not merged to master, or that are on branches that have been deleted already.

Specifications

• python-gitlab version: 1.5.1
• API version you are using (v3/v4): v4
• Gitlab server version (or gitlab.com): GitLab Community Edition 11.0.4 edb037c