Explicit error message for corpus_id type in check_required_types

arkindex_worker/worker/element.py

 # -*- coding: utf-8 -*-
 
+import uuid
 
 from peewee import IntegrityError
 
@@ -20,6 +21,9 @@ class ElementMixin(object):
         Check that a corpus has a list of required element types,
         and raise an exception if any of them are missing.
         """
+        assert isinstance(
+            corpus_id, (uuid.UUID, str)
+        ), "Corpus ID should be a string or UUID"
         assert len(type_slugs), "At least one element type slug is required."
         assert all(
             isinstance(slug, str) for slug in type_slugs