service: error when published record without draft

* Raise a proper error when trying to read a draft for a published
  record when it's not being edited (i.e draft doesn't exists).

invenio_drafts_resources/services/records/service.py

@@ -11,6 +11,7 @@
 
 from flask import current_app
 from invenio_db import db
+from invenio_pidstore.errors import PIDDoesNotExistError
 from invenio_records_resources.services import LinksTemplate
 from invenio_records_resources.services import RecordService as RecordServiceBase
 from invenio_records_resources.services import ServiceSchemaWrapper
@@ -197,7 +198,15 @@ def search_versions(
     def read_draft(self, identity, id_, expand=False):
         """Retrieve a draft."""
         # Resolve and require permission
-        draft = self.draft_cls.pid.resolve(id_, registered_only=False)
+        try:
+            draft = self.draft_cls.pid.resolve(id_, registered_only=False)
+        except NoResultFound:
+            # Happens when record is published and not being edited (i.e. PID
+            # with object id exists for the published record, but object
+            # getter fails to get the draft object because only the record
+            # object exists).
+            raise PIDDoesNotExistError(self.draft_cls.pid.field._pid_type, id_)
+
         self.require_permission(identity, "read_draft", record=draft)
 
         # Run components

tests/services/test_record_service.py

@@ -131,7 +131,7 @@ def test_publish_draft(app, service, identity_simple, input_data):
         assert record[key] == value
 
     # Check draft deletion
-    with pytest.raises(NoResultFound):
+    with pytest.raises(PIDDoesNotExistError):
         # NOTE: Draft and Record have the same `id`
         draft = service.read_draft(identity_simple, record.id)