Generators/Async Generators with TReturn type argument which extends undefined have a return method with a non-optional argument in 3.6.2

TypeScript Version: 3.6.2

Search Terms:
generator iterator return argument optional required

Code

function *gen(): Generator<number, number | undefined> {
  yield 1;
  return 2;
}

gen().return();

Expected behavior:
The argument passed to the return method should be optional. Not sure if this is possible with typescript.

Actual behavior:

file.ts(6,7): error TS2554: Expected 1 arguments, but got 0.
6 gen().return();
        ~~~~~~~~

  typescript/lib/lib.es2015.generator.d.ts:26:12
    26     return(value: TReturn): IteratorResult<T, TReturn>;
                  ~~~~~~~~~~~~~~
    An argument for 'value' was not provided.

Playground Link:

Playground is not available for 3.6.2

Related Issues:
#30790 Strongly typed iterator PR.
#32682 Other (async) iterator usability issues.
#33239 Trouble implementing async iterator interface in 3.6.2
#33241 Unable to use done property of IteratorResult to narrow types in typescript 3.6.2