Matched DistributionTree serializers with the models

https://pulp.plan.io/issues/7394
closes #7394

[nocoverage]

(cherry picked from commit 515057f)

CHANGES/7394.bugfix

@@ -0,0 +1 @@
+Fixing OpenAPI schema for Variant

pulp_rpm/app/serializers/distribution.py

@@ -75,19 +75,19 @@ class VariantSerializer(serializers.ModelSerializer):
         help_text=_("Relative path to directory with binary RPMs.")
     )
     source_packages = serializers.CharField(
-        help_text=_("Relative path to directory with source RPMs.")
+        help_text=_("Relative path to directory with source RPMs."), allow_null=True
     )
     source_repository = serializers.CharField(
-        help_text=_("Relative path to YUM repository with source RPMs.")
+        help_text=_("Relative path to YUM repository with source RPMs."), allow_null=True
     )
     debug_packages = serializers.CharField(
-        help_text=_("Relative path to directory with debug RPMs.")
+        help_text=_("Relative path to directory with debug RPMs."), allow_null=True
     )
     debug_repository = serializers.CharField(
-        help_text=_("Relative path to YUM repository with debug RPMs.")
+        help_text=_("Relative path to YUM repository with debug RPMs."), allow_null=True
     )
     identity = serializers.CharField(
-        help_text=_("Relative path to a pem file that identifies a product.")
+        help_text=_("Relative path to a pem file that identifies a product."), allow_null=True
     )
 
     class Meta:

pulp_rpm/tests/functional/api/test_sync.py

@@ -63,6 +63,7 @@
 from pulp_rpm.tests.functional.utils import set_up_module as setUpModule  # noqa:F401
 
 from pulpcore.client.pulp_rpm import (
+    ContentDistributionTreesApi,
     RepositoriesRpmApi,
     RpmRepositorySyncURL,
     RemotesRpmApi,
@@ -254,6 +255,10 @@ def test_kickstarter(self):
         # sync again
         repo, remote = self.do_test(repository=repo, remote=remote)
 
+        # Test distribution tree API
+        dist_tree_api = ContentDistributionTreesApi(self.client)
+        self.assertEqual(dist_tree_api.list().results[0].release_short, "RHEL")
+
         # Check that nothing has changed since the last sync.
         self.assertDictEqual(get_content_summary(repo.to_dict()), RPM_KICKSTART_FIXTURE_SUMMARY)
         self.assertEqual(latest_version_href, repo.latest_version_href)