diff --git a/swh/storage/cassandra/storage.py b/swh/storage/cassandra/storage.py
--- a/swh/storage/cassandra/storage.py
+++ b/swh/storage/cassandra/storage.py
@@ -462,7 +462,7 @@
 
         return {"revision:add": len(revisions)}
 
-    def revision_missing(self, revisions):
+    def revision_missing(self, revisions: List[Sha1Git]) -> Iterable[Sha1Git]:
         return self._cql_runner.revision_missing(revisions)
 
     def revision_get(self, revisions):
diff --git a/swh/storage/in_memory.py b/swh/storage/in_memory.py
--- a/swh/storage/in_memory.py
+++ b/swh/storage/in_memory.py
@@ -522,7 +522,7 @@
 
         return {"revision:add": count}
 
-    def revision_missing(self, revisions):
+    def revision_missing(self, revisions: List[Sha1Git]) -> Iterable[Sha1Git]:
         for id in revisions:
             if id not in self._revisions:
                 yield id
diff --git a/swh/storage/interface.py b/swh/storage/interface.py
--- a/swh/storage/interface.py
+++ b/swh/storage/interface.py
@@ -508,11 +508,11 @@
         ...
 
     @remote_api_endpoint("revision/missing")
-    def revision_missing(self, revisions):
+    def revision_missing(self, revisions: List[Sha1Git]) -> Iterable[Sha1Git]:
         """List revisions missing from storage
 
         Args:
-            revisions (iterable): revision ids
+            revisions: revision ids
 
         Yields:
             missing revision ids
diff --git a/swh/storage/storage.py b/swh/storage/storage.py
--- a/swh/storage/storage.py
+++ b/swh/storage/storage.py
@@ -604,9 +604,11 @@
 
     @timed
     @db_transaction_generator()
-    def revision_missing(self, revisions, db=None, cur=None):
+    def revision_missing(
+        self, revisions: List[Sha1Git], db=None, cur=None
+    ) -> Iterable[Sha1Git]:
         if not revisions:
-            return
+            return None
 
         for obj in db.revision_missing_from_list(revisions, cur):
             yield obj[0]