diff --git a/aiogram/utils/payload.py b/aiogram/utils/payload.py
index 5254fa44..dfef3db1 100644
--- a/aiogram/utils/payload.py
+++ b/aiogram/utils/payload.py
@@ -15,7 +15,9 @@ def generate_payload(exclude=None, **kwargs):
 
 
 def prepare_arg(value):
-    if isinstance(value, (list, dict)):
+    if value is None:
+        return None
+    elif isinstance(value, (list, dict)):
         return json.dumps(value)
     elif hasattr(value, 'to_json'):
         return json.dumps(value.to_json())