fix: constructor with default values as objects

[MrMeshok]

While working on #187 I noticed what you can't map to a class that has constructor with default values as objects if source missing these arguments.
Seems like a complex issue to fix, so I'll start with the tests

[joelwurtz]

Indeed, this will be hard to fix, there is 3 possible things to do :

• disallow this (throw an exception if it happens so we dont let user in weird state)
• allow this only if value can be cloned (but we will have new issue with sub property that have object and may be not cloned)
• having a way to parse this code and reproduce it when generating (reproducing is easy, parsing i don't have a way in mind right now but should be feasible)

wdyt @Korbeil @nikophil ?

[MrMeshok]

Actually, there is a simple way.
Instead of this:

$constructorarg_1 = $source->author ?? Author::__set_state();

$item = new Post(author: $constructorarg_1)

It should be this:

$constructorargs = [];
if (isset($source->author)) {
    $constructorargs['author'] = $source->author;
}

$item = new Post(...$constructorargs)