"Merge" button inactive on branch without pipeline - "You can only merge once the items above are resolved" - regression in 12.1

Summary

"Merge" button inactive on branch without pipeline - "You can only merge once the items above are resolved" - regression in gitlab 12.1 CE

Steps to reproduce

1. Create repository with at least 2 branches - for example "master" and branch "test"
2. Branch "master" has .gitlab-ci.yml file present = has build pipeline, but branch "test" has no such file (requires no pipeline to merge)
3. In project -> settings -> general -> Merge Request - make sure option "pipeline must succeed is enabled (checked)" for this repository project
4. Create new branch "sample-branch/test" from branch "test", make some changes, and create new merge request to merge this branch into branch "test"

What is the current bug behavior?

Cannot "merge such merge request - button "Merge" is disabled and "You can only merge once the items above are resolved" message is displayed.

What is the expected correct behavior?

It should be possible to merge such merge request. It worked in versions 11.X of gitlab ce. Even if option "pipeline must succeed" is enabled it should work only for branches with pipelines.

Relevant logs and/or screenshots