Untitled

def unlock(self, key: str) -> str | None:
    # If the key doesn't exist in the database and isn't currently locked, it's an invalid request.
    if key not in self.db and key not in self.locks:
        return "invalid_request"

    # If the key exists but is not locked, return None.
    if key not in self.locks:
        return None

    # Handle the lock release
    self.locks.pop(key)

    # If there are users waiting in the queue for this key, assign the lock to the next user.
    if key in self.lock_queues and self.lock_queues[key]:
        next_user = self.lock_queues[key].popleft()
        self.locks[key] = next_user
        return "released"

    # If there are no more users in the queue, clean up the queue.
    if key in self.lock_queues:
        del self.lock_queues[key]

    return "released"