flutter_vap library Null safety

Classes

QueueUtil
https://github.com/qq326646683/tech-article/blob/master/flutter/Flutter%E4%B8%8A%E7%BA%BF%E9%A1%B9%E7%9B%AE%E5%AE%9E%E6%88%98%E2%80%94%E2%80%94%E9%98%9F%E5%88%97%E4%BB%BB%E5%8A%A1.md
VapController
VapView