2.x cryptic error on empty queue

[urugator]

new Relay([])->handle($request);
results in
Uncaught Error: Function name must be a string

https://github.com/relayphp/Relay.Relay/blob/2.x/src/Runner.php#L31
$entry becomes false

[niden]

From my understanding this appears because $middleware is false. When the queue is empty the last middleware is called like this

$middleware($request, $this)

There is no last or any middleware so this appears.

Look at the tests here: https://github.com/relayphp/Relay.Relay/blob/2.x/tests/RelayTest.php#L41