diff --git a/backend/src/appointment/exceptions/validation.py b/backend/src/appointment/exceptions/validation.py
index 394adefe4..d56640a79 100644
--- a/backend/src/appointment/exceptions/validation.py
+++ b/backend/src/appointment/exceptions/validation.py
@@ -207,7 +207,7 @@ class RemoteCalendarConnectionError(APIException):
     status_code = 400
     reason = None
 
-    def __init__(self, reason: str|None, **kwargs):
+    def __init__(self, reason: str|None = None, **kwargs):
         if reason:
             self.reason = reason
         super().__init__(**kwargs)