Default branch is not preserved when importing external repo from GitHub

Summary

When importing a Git repo from GitHub to GitLab, the default branch is not preserved

Steps to reproduce

1. Import external Git repo from GitHub where default branch has been changed
2. Verify default branch is not preserved

What is the current bug behavior?

Default branch is always set to master on import

What is the expected correct behavior?

Default branch should be preserved on import

Possible fixes