sqlalchemy.exc.InvalidRequestError: This Session's transaction has been rolled back due to a previous exception during flush. To begin a new transaction with this Session, first issue Session.rollback(). Original exception was: (sqlite3.IntegrityError) NOT NULL constraint failed: follows.follower_id [SQL: 'INSERT INTO follows (followed_id, timestamp) VALUES (?, ?)'] [parameters: (100, '2017-09-08 07:31:07.391094')]

执行关注操作的时候报错