Description of problem:
Upgrade to 6.14 fails on rpm.0048_artifacts_dependencies_fix migration with TypeError: 'NoneType' object is not subscriptable

Version-Release number of selected component (if applicable):
6.14.0 Snap 3 (regression against Snap 2)
python39-pulp-rpm-3.19.2-1.el8pc.noarch

How reproducible:
always with some pulp data

Steps to Reproduce:
1. Upgrade 6.13 to 6.14.0

...
2023-06-08 07:01:36 [ERROR ] [configure] /Stage[main]/Pulpcore::Database/Pulpcore::Admin[migrate --noinput]/Exec[pulpcore-manager migrate --noinput]/returns: change from 'notrun' to ['0'] failed: 'pulpcore-manager migrate --noinput' returned 1 instead of one of [0]


Actual results:
upgrade fails on pulpcore migration

Expected results:
upgrade finishes successfully

Additional info:
Operations to perform:
  Apply all migrations: ansible, auth, certguard, container, contenttypes, core, file, rpm, sessions
Running migrations:
  Applying ansible.0046_add_fulltext_search_fix... OK
  Applying core.0095_artifactdistribution... OK
  Applying core.0096_alter_task_logging_cid... OK
  Applying core.0097_remove_telemetry_task_schedule... OK
  Applying core.0098_pulp_labels... OK
  Applying file.0015_allow_null_manifest... OK
  Applying rpm.0046_rbac_perms... OK
  Applying rpm.0047_modulemd_datefield... OK
  Applying rpm.0048_artifacts_dependencies_fix...Traceback (most recent call last):
  File "/usr/bin/pulpcore-manager", line 33, in <module>
    sys.exit(load_entry_point('pulpcore==3.22.2', 'console_scripts', 'pulpcore-manager')())
  File "/usr/lib/python3.9/site-packages/pulpcore/app/manage.py", line 11, in manage
    execute_from_command_line(sys.argv)
  File "/usr/lib/python3.9/site-packages/django/core/management/__init__.py", line 419, in execute_from_command_line
    utility.execute()
  File "/usr/lib/python3.9/site-packages/django/core/management/__init__.py", line 413, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/lib/python3.9/site-packages/django/core/management/base.py", line 354, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/lib/python3.9/site-packages/django/core/management/base.py", line 398, in execute
    output = self.handle(*args, **options)
  File "/usr/lib/python3.9/site-packages/django/core/management/base.py", line 89, in wrapped
    res = handle_func(*args, **kwargs)
  File "/usr/lib/python3.9/site-packages/django/core/management/commands/migrate.py", line 244, in handle
    post_migrate_state = executor.migrate(
  File "/usr/lib/python3.9/site-packages/django/db/migrations/executor.py", line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/usr/lib/python3.9/site-packages/django/db/migrations/executor.py", line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/usr/lib/python3.9/site-packages/django/db/migrations/executor.py", line 227, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/usr/lib/python3.9/site-packages/django/db/migrations/migration.py", line 126, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/usr/lib/python3.9/site-packages/django/db/migrations/operations/special.py", line 190, in database_forwards
    self.code(from_state.apps, schema_editor)
  File "/usr/lib/python3.9/site-packages/pulp_rpm/app/migrations/0048_artifacts_dependencies_fix.py", line 31, in fixup_modulemd_artifacts_dependencies
    mmd.artifacts = modulemd["data"].get("artifacts", {}).get("rpms", [])
TypeError: 'NoneType' object is not subscriptable