Some of these missing checks were why Flow was an attractive choice when weighing [Flow vs Typescript][1].

For example, it wasn't until Typescript 2.0 that we got null checks!

- https://www.typescriptlang.org/docs/handbook/release-notes/t...

  function getLength(s: string): number {
    return s.length; //  Runtime crash if s is null/undefined
  }
  
  getLength(null); // TypeScript <2.0 would not error here

[1]: https://djcordhose.github.io/flow-vs-typescript/2016_hhjs.ht...