diff --git a/opcua/server/address_space.py b/opcua/server/address_space.py
index a0901e70d..517d6a61a 100644
--- a/opcua/server/address_space.py
+++ b/opcua/server/address_space.py
@@ -463,6 +463,8 @@ def _call(self, method):
                 res.StatusCode = ua.StatusCode(ua.StatusCodes.BadNothingToDo)
             else:
                 try:
+                    if method.InputArguments is None:
+                        method.InputArguments = [] 
                     result = node.call(method.ObjectId, *method.InputArguments)
                     if isinstance(result, ua.CallMethodResult):
                         res = result
diff --git a/tests/tests_subscriptions.py b/tests/tests_subscriptions.py
index 9943eb8eb..be6c916cc 100644
--- a/tests/tests_subscriptions.py
+++ b/tests/tests_subscriptions.py
@@ -128,7 +128,7 @@ def test_subscription_count_list(self):
             val = copy(val)  # we do not want to modify object in our db, we need a copy in order to generate event
             val.append(i)
             var.set_value(copy(val))
-        time.sleep(0.2)  # let last event arrive
+        time.sleep(0.3)  # let last event arrive
         self.assertEqual(myhandler.datachange_count, nb + 1)
         sub.delete()