diff --git a/kallithea/model/db.py b/kallithea/model/db.py
--- a/kallithea/model/db.py
+++ b/kallithea/model/db.py
@@ -1388,7 +1388,7 @@ class Repository(Base, BaseModel):
             .filter(ChangesetComment.repo == self)
         if revisions is not None:
             if not revisions:
-                return [] # don't use sql 'in' on empty set
+                return {} # don't use sql 'in' on empty set
             cmts = cmts.filter(ChangesetComment.revision.in_(revisions))
         grouped = collections.defaultdict(list)
         for cmt in cmts.all():