Attempting to import public Github repository results in import hanging

Issue Summary

On Bitbucket 6.7+, when attempting to import a public repository

Steps to Reproduce

1. Create a new project
2. Choose Import Repository
3. Choose the "Git" option, and input a public github clone URL with no credentials specified
4. Confirm the import

Expected Results

• Progress bar gradually goes to 100%, then you are placed on the project overview page - and the repository is successfully created

Actual Results

• Progress bar stays stuck at around 15%, and if you refresh the page you get directed to the project overview page. If you click on the new repository, the repository presents you with the following page:
  • 

The following debug lines can be seen continually repeating in the in the atlassian-bitbucket.log file:

2019-11-22 04:58:10,435 DEBUG [http-nio-7990-exec-24] eslaughter @7D4GFSx298x25151x0 1xiz5m6 192.168.5.1,192.168.5.2 "GET /plugins/servlet/import-in-process/projects/TEST3/repos/go-jira HTTP/1.1" c.a.s.internal.scm.git.RawGitAgent /var/atlassian/application-data/stash/shared/data/repositories/163: No packed refs found (packed-refs exists: false; lines checked: 0)
2019-11-22 04:58:10,435 DEBUG [http-nio-7990-exec-24] eslaughter @7D4GFSx298x25151x0 1xiz5m6 192.168.5.1,192.168.5.2 "GET /plugins/servlet/import-in-process/projects/TEST3/repos/go-jira HTTP/1.1" c.a.s.internal.scm.git.RawGitAgent 163: No loose refs found ('refs/' exists: true, Directories checked: 3)
2019-11-22 04:58:10,435 DEBUG [http-nio-7990-exec-24] eslaughter @7D4GFSx298x25151x0 1xiz5m6 192.168.5.1,192.168.5.2 "GET /plugins/servlet/import-in-process/projects/TEST3/repos/go-jira HTTP/1.1" c.a.s.internal.scm.git.RawGitAgent TEST3/go-jira[163]: Repository is empty

The repository will remain in this state until Bitbucket is restarted - at which point, once Bitbucket comes back up the repository will no longer exist.

Workaround

Create a Github account, and fork the repository to be owned by your user - and complete the import using the official "Github" import option by inputting your Github username and personal access token.