Resolve Missing Repository Error During Migration

What does this MR do and why?

This MR prevents repository import from running if the incoming project has no repository

Screenshots or screen recordings

These are strongly recommended to assist reviewers and reduce the time to merge your change.

How to set up and validate locally

1. Import a group with empty projects with feature flag :bulk_import_projects enabled
2. Check the server exception log for NoMethodError undefined method start_with?' for nil:NilClass`. This should not appear with these changes

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #343686 (closed)