// ofEmpty refers Optional#empty() in java
// It is renamed as ofEmpty() because of empty() is reserved by PHP 
Optional::ofEmpty()->isPresent(); // false

Optional::of("value")->orElse("elseValue"); // value
 
Optional::ofEmpty()->orElseThrow(function () { throw .... }); // throws exception

Optional::ofEmpty()->filter(function ($a) { return (int) $a; }); // function is not executed

Optional::of(5)->map(function ($a) { return $a * 2; })->get(); // returns 10

Optional::ofEmpty()->orElseGet(function () { return 10; }); // returns 10