Pull mirror from Bitbucket fails

Summary

I cloned my repo into GitLab (SaaS - Bronze plan) from bitbucket over HTTPS, which was successful. Then I tried to setup a mirror (pull) to pull into Gitlab, all changes made to bitbucket. I entered the right details ,ie, the URL of the repo and the password but the mirroring fails and throws the following error undefined method each_with_object' for "objects":String

— https://stackoverflow.com/questions/56052115/gitlab-mirroring-feature-doesnt-work-when-pulling-from-a-remote-repo

Example Project

Details in ZD: https://gitlab.zendesk.com/agent/tickets/121045 (internal)

What is the current bug behavior?

The repository fails to update: undefined method each_with_object' for "objects":String

What is the expected correct behavior?

Mirroring succeeds

Relevant logs and/or screenshots

https://log.gitlab.net/goto/eef99f448c8cfc19c87210fb823e50ee

Output of checks

This bug happens on GitLab.com