From 2de97bc97891f88a56653fd583fe3635830afa2a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=A9r=C3=B4me=20Lafr=C3=A9choux?=
 <jlafrechoux@nobatek.inef4.com>
Date: Thu, 8 Sep 2022 18:54:00 +0200
Subject: [PATCH] Fix Field._serialize typing

---
 src/marshmallow/fields.py | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/src/marshmallow/fields.py b/src/marshmallow/fields.py
index 5611b24a4..52d13dcf7 100644
--- a/src/marshmallow/fields.py
+++ b/src/marshmallow/fields.py
@@ -387,7 +387,9 @@ def _bind_to_schema(self, field_name, schema):
             self.parent.root if isinstance(self.parent, FieldABC) else self.parent
         )
 
-    def _serialize(self, value: typing.Any, attr: str, obj: typing.Any, **kwargs):
+    def _serialize(
+        self, value: typing.Any, attr: str | None, obj: typing.Any, **kwargs
+    ):
         """Serializes ``value`` to a basic Python datatype. Noop by default.
         Concrete :class:`Field` classes should implement this method.