$CI_ENVIRONMENT_SLUG is not set for branches with a '+' in the name

Summary

For a branch name like so: sa+ck/some-changes-STORY-ID, $CI_ENVIRONMENT_SLUG is blank.

Steps to reproduce

  • Create a branch with a + in the name. Example: pair1+pair2/some-changes

Example Project

screenshot

What is the current bug behavior?

$CI_ENVIRONMENT_SLUG is blank

What is the expected correct behavior?

$CI_ENVIRONMENT_SLUG should not be blank, it should be a URL-safe string.

Relevant logs and/or screenshots

screenshot

Output of checks

This bug happens on GitLab.com