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
@@ -1314,11 +1314,11 @@
         else:
             return None
 
-    def clear_buffers(self, object_types: Sequence[str]) -> None:
+    def clear_buffers(self, object_types: Sequence[str] = ()) -> None:
         """Do nothing
 
         """
         return None
 
-    def flush(self, object_types: Sequence[str]) -> Dict[str, int]:
+    def flush(self, object_types: Sequence[str] = ()) -> Dict[str, int]:
         return {}
diff --git a/swh/storage/interface.py b/swh/storage/interface.py
--- a/swh/storage/interface.py
+++ b/swh/storage/interface.py
@@ -1185,7 +1185,7 @@
         ...
 
     @remote_api_endpoint("clear/buffer")
-    def clear_buffers(self, object_types: Sequence[str]) -> None:
+    def clear_buffers(self, object_types: Sequence[str] = ()) -> None:
         """For backend storages (pg, storage, in-memory), this is a noop operation. For proxy
         storages (especially filter, buffer), this is an operation which cleans internal
         state.
@@ -1193,7 +1193,7 @@
         """
 
     @remote_api_endpoint("flush")
-    def flush(self, object_types: Sequence[str]) -> Dict[str, int]:
+    def flush(self, object_types: Sequence[str] = ()) -> Dict[str, int]:
         """For backend storages (pg, storage, in-memory), this is expected to be a noop
         operation. For proxy storages (especially buffer), this is expected to trigger
         actual writes to the backend.
diff --git a/swh/storage/postgresql/storage.py b/swh/storage/postgresql/storage.py
--- a/swh/storage/postgresql/storage.py
+++ b/swh/storage/postgresql/storage.py
@@ -1396,13 +1396,13 @@
             return None
         return MetadataAuthority.from_dict(dict(zip(db.metadata_authority_cols, row)))
 
-    def clear_buffers(self, object_types: Sequence[str]) -> None:
+    def clear_buffers(self, object_types: Sequence[str] = ()) -> None:
         """Do nothing
 
         """
         return None
 
-    def flush(self, object_types: Sequence[str]) -> Dict[str, int]:
+    def flush(self, object_types: Sequence[str] = ()) -> Dict[str, int]:
         return {}
 
     def _get_authority_id(self, authority: MetadataAuthority, db, cur):
diff --git a/swh/storage/tests/test_postgresql.py b/swh/storage/tests/test_postgresql.py
--- a/swh/storage/tests/test_postgresql.py
+++ b/swh/storage/tests/test_postgresql.py
@@ -248,13 +248,13 @@
         """Calling clear buffers on real storage does nothing
 
         """
-        assert swh_storage.clear_buffers([]) is None
+        assert swh_storage.clear_buffers() is None
 
     def test_flush(self, swh_storage):
         """Calling clear buffers on real storage does nothing
 
         """
-        assert swh_storage.flush([]) == {}
+        assert swh_storage.flush() == {}
 
     def test_dbversion(self, swh_storage):
         with swh_storage.db() as db: