Map::get(): argument fallback value

[aubryfr]

Am I right that that the fallback value for $default in Map::get() can never be used?
https://github.com/php-ds/polyfill/blob/master/src/Map.php#L320

If the method is called without its second argument (to get the fallback value), the call will fail here (as confirmed by the testGetKeyNotFound test).

In that case, I'd say it should be removed from the signature.

(Or maybe there's a PHP trick that I'm not thinking about?)