Gitlab merge request issue on git-clone step

Hi @viktorbenei and @kdobmayer , I am currently having this issues with my builds. When I create a merge(pull) request on gitlab, the webhook triggers the build however the build fails at due to:

git "init"
Initialized empty Git repository in /Users/vagrant/git/.git/
git "remote" "add" "origin" "git@gitlab.com:X/Y.git"
git "fetch" "origin" "master"
Warning: Permanently added 'gitlab.com,xx.xxx.xxx.xxx' (ECDSA) to the list of known hosts.
From gitlab.com:X/Y
 * branch            master     -> FETCH_HEAD
 * [new branch]      master     -> origin/master
ERROR: auto merge, error: there is no Pull Request branch and can't download diff file
|                                                                              |
+---+---------------------------------------------------------------+----------+
| x | git-clone@4.0.10 (exit code: 1)                               | 9.14 sec |
+---+---------------------------------------------------------------+----------+

I am making a merge request from a private repo to another private repo. I have used the generate SSH keypair to copy the ssh public key from bitrise to both private repos and I still get the above.

To note, when I create a merge request within the same repo, it works as expected.