The Pulp 2 to Pulp 3 migration fails with error "NoMethodError: undefined method `link?' for nil:NilClass" in Red Hat Satellite 6.9

Issue

• The attempt to perform Pulp 2 to Pulp 3 migration via the satellite-maintain content prepare command fails with the following error:

  Prepare content for Pulp 3:
  Checking for valid Katello configuration.
  Starting task.
  
  2022-04-01 08:11:23 -0400: Content migration starting. These steps may take a while to complete. Refer to `foreman-maintain content migration-stats` for an estimate.Migration failed, You will want to investigate: https://satellite.example.com/foreman_tasks/tasks/fa9130c3-5660-46cb-82ea-a03389e27968
  rake aborted!
  ForemanTasks::TaskError: Task fa9130c3-5660-46cb-82ea-a03389e27968: NoMethodError: undefined method `link?' for nil:NilClass
  /opt/theforeman/tfm/root/usr/share/gems/gems/katello-3.18.1.50/lib/katello/tasks/pulp3_migration.rake:43:in `block (2 levels) in <top (required)>'
  /opt/rh/rh-ruby25/root/usr/share/gems/gems/rake-12.3.3/exe/rake:27:in `<top (required)>'
  Tasks: TOP => katello:pulp3_migration
  (See full trace by running task with --trace)
                                                                       [FAIL]
  Failed executing preserve_output=true foreman-rake katello:pulp3_migration, exit status 1