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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def find_identity(session, id_):
 """Find an identity. Find an identity by its ID using the given `session`. When the identity does not exist the function will return `None`. :param session: database session :param id_: id of the identity to find :returns: an identity object; `None` when the identity does not exist """

    identity = session.query(Identity). \
        filter(Identity.id == id_).first()

    return identity