Add default error value to context in collection_case_priors view to prevent variable resolution issues

atlas/views.py

@@ -3165,6 +3165,9 @@ def collection_case_priors(request, exam_id, case_number):
             "added_priors": added_priors,
             "available_priors": available_priors,
             "can_edit": can_edit,
+            # Provide a default `error` value so `{% if error %}` checks in included
+            # partials won't raise during variable resolution when the key is absent.
+            "error": None,
         },
     )