ss:`~gridfs.grid_file.GridOut`,
        or ``None`` if no matching file is found. For example::

            file = fs.find_one({"filename": "lisa.txt"})

        :Parameters:
          - `filter` (optional): a dictionary specifying
            the query to be performing OR any other type to be used as
            the value for a query for ``"_id"`` in the file collection.
          - `*args` (optional): any additional positional arguments are
            the same as the arguments to :meth:`find`.
          - `session` (optional): a
            :class:`~pymongo.client_session.ClientSession`
          - `**kwargs` (optional): any additional keyword arguments
            are the same as the arguments to :meth:`find`.

        .. versionchanged:: 3.6
           Added ``session`` parameter.
        Nr8