Chained promise returning nothing should be OK

[g105b]

Typical fetch:

$http->fetch("http://example.com")

->then(function(Response $response) {
  if(!$response->ok) {
    return; // HERE LIES AN ISSUE
  }

  return $response->text();
})

->then(function(string $html) {
  // ...
});

Because the next promise in the chain expects a string of html, it's impossible to return nothing.

What's the proper way of returning early? Should we be able to return void at this point?