fix: correct return type annotation for find_one_and_update to include None

Author: cj81499

doc/changelog.rst

@@ -17,6 +17,7 @@ PyMongo 4.16 brings a number of changes including:
 - Removed support for Eventlet.
   Eventlet is actively being sunset by its maintainers and has compatibility issues with PyMongo's dnspython dependency.
 - Use Zstandard support from the standard library for Python 3.14+, and use ``backports.zstd`` for older versions.
+- Fixed return type annotation for :meth:`~pymongo.asynchronous.collection.AsyncCollection.find_one_and_update` and :meth:`~pymongo.synchronous.collection.Collection.find_one_and_update` to include ``None``.
 
 Changes in Version 4.15.4 (2025/10/21)
 --------------------------------------

doc/contributors.rst

@@ -107,3 +107,4 @@ The following is a list of people who have contributed to
 - Jeffrey A. Clark (aclark4life)
 - Steven Silvester (blink1073)
 - Noah Stapp (NoahStapp)
+- Cal Jacobson (cj81499)

pymongo/asynchronous/collection.py

@@ -3510,7 +3510,7 @@ async def find_one_and_update(
         let: Optional[Mapping[str, Any]] = None,
         comment: Optional[Any] = None,
         **kwargs: Any,
-    ) -> _DocumentType:
+    ) -> Optional[_DocumentType]:
         """Finds a single document and updates it, returning either the
         original or the updated document.
 

pymongo/synchronous/collection.py

@@ -3503,7 +3503,7 @@ def find_one_and_update(
         let: Optional[Mapping[str, Any]] = None,
         comment: Optional[Any] = None,
         **kwargs: Any,
-    ) -> _DocumentType:
+    ) -> Optional[_DocumentType]:
         """Finds a single document and updates it, returning either the
         original or the updated document.