...instead of throwing a syntax error due to attempting to JSON parse ''.

let fetch = require('node-fetch');
fetch('http://httpbin.org/status/204').then(res => res.json()).then(object => {
    console.log(object);
}).catch(error => console.error(error));

Demo: http://runkit.com/dandv/node-fetch-204-no-content

Fixing this would attain compatibility with request and got.

More generally, it would be more tolerant to return an empty object if the response is the empty string (regardless of the status code being 204 or other 2xx).