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
@@ -507,12 +507,11 @@
 
         Yields:
             dicts with the same keys as those given to `release_add`
-
-        Raises:
-            ValueError: if the keys does not match (url and type) nor id.
+            (or ``None`` if a release does not exist)
 
         """
-        yield from map(self._releases.__getitem__, releases)
+        for rel_id in releases:
+            yield copy.deepcopy(self._releases.get(rel_id))
 
     def snapshot_add(self, origin, visit, snapshot):
         """Add a snapshot for the given origin/visit couple
diff --git a/swh/storage/storage.py b/swh/storage/storage.py
--- a/swh/storage/storage.py
+++ b/swh/storage/storage.py
@@ -720,15 +720,14 @@
 
         Yields:
             dicts with the same keys as those given to `release_add`
-
-        Raises:
-            ValueError: if the keys does not match (url and type) nor id.
+            (or ``None`` if a release does not exist)
 
         """
         for release in db.release_get_from_list(releases, cur):
-            yield converters.db_to_release(
+            data = converters.db_to_release(
                 dict(zip(db.release_get_cols, release))
             )
+            yield data if data['target_type'] else None
 
     @db_transaction()
     def snapshot_add(self, origin, visit, snapshot,
diff --git a/swh/storage/tests/test_storage.py b/swh/storage/tests/test_storage.py
--- a/swh/storage/tests/test_storage.py
+++ b/swh/storage/tests/test_storage.py
@@ -908,6 +908,11 @@
                           self.normalize_entity(self.release2)],
                          [actual_releases[0], actual_releases[1]])
 
+        unknown_releases = \
+            list(self.storage.release_get([self.release3['id']]))
+
+        self.assertIsNone(unknown_releases[0])
+
     def test_origin_add_one(self):
         origin0 = self.storage.origin_get(self.origin)
         self.assertIsNone(origin0)