"All project roles are empty" blocker in JCMA pre-flight checks

Issue Summary

This is reproducible on Data Center: yes

When we include a project in migration plan which doesn't have project roles associated with it, then the preflight checks failed, blocking the migration.

Steps to Reproduce

1. Create a project in Jira Server
2. Make sure no projects roles are associated with this project
3. Create a migration plan with this project and start the pre-flight checks
4. Data preparation error Pre-flight check failed, with the error "All project roles are empty"

Workaround

Associate a project role with the project.