BitBucket Server Importer: Commits/Changes Missing From Imported Pull Requests

Summary

When pull requests that contain squashed commits are imported into GitLab from BitBucket Server, the corresponding merge requests are showing empty Commits and Changes tabs.

Steps to reproduce

• Commit to a BitBucket Server repo.
• Squash and merge your commit.
• Import the BitBucket repo into GitLab via the UI importer.
• View the empty Commits and Changes tabs in the associated merge request.

Example Project

N/A

What is the current bug behavior?

Commits and changes aren't showing up for BitBucket pull requests that are imported into GitLab.

What is the expected correct behavior?

Commits and changes from squashed commits being successfully imported into GitLab and displayed in merge requests.

Further Context

Zendesk ticket: https://gitlab.zendesk.com/agent/tickets/274285

Slack thread: https://gitlab.slack.com/archives/CLX7WMSKW/p1646947692657169