diff --git a/api/s0_base.py b/api/s0_base.py
index e984143..6588846 100644
--- a/api/s0_base.py
+++ b/api/s0_base.py
@@ -123,7 +123,7 @@ def delete_node(name: str, node_type: str, id: str, table_sql: str, table_undo_s
         cur.execute(f"select * from coordinates where node = '{id}'")
         row = cur.fetchone()
         if row == None:
-            return
+            return ChangeSet()
 
         coord = row['coord']
 
diff --git a/api/s7_valves.py b/api/s7_valves.py
index 496045c..7146562 100644
--- a/api/s7_valves.py
+++ b/api/s7_valves.py
@@ -75,11 +75,11 @@ def get_valve_minor_loss(name: str, id: str) -> float | None:
 
 def _set_valve(name: str, id: str, key: str, key_type: str, value: str, optional: bool = False) -> ChangeSet:
     if not is_valve(name, id):
-        return
+        return ChangeSet()
 
     row = _get_valve(name, id)
     if row == None:
-        return
+        return ChangeSet()
 
     return update(name, VALVE, 'valves', 'id', id, key, key_type, row[key], value, optional)