First argument to fetch is optional, but fetch requires at least 1 arg

[JakeTunaley]

TypeScript Version: 3.0.0-dev.20180707

Search Terms: fetch lib

Code

fetch();

Expected behavior:

An error: Expected 1 arguments, but got 0.

Actual behavior:

No errors are emitted. This is non-compliant with the fetch spec, wherein only the second argument is optional.

Playground Link: http://www.typescriptlang.org/play/index.html#src=fetch()%3B