Follow-up from "Resolve "pipeline_schedules pages throwing error 500""

What does this MR do?

This MR add a patch for the case "when pipeline_schedule.ref is empty(i.e. "")". This issue was originally addressed at https://gitlab.com/gitlab-org/gitlab-ce/issues/32790, however, the patch we released was not sufficient to cover this case.

Are there points in the code the reviewer needs to double check?

IS this MR sufficient?

Why was this MR needed?

Because it's regression.

Screenshots (if relevant)

N/A

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/35345 Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/32790 Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/34652