Nullable enum cast

[juliomotol]

Given the ff setting class:

class FooSettings extends Settings
{
    public ?DummyEnum $enum = null;

    public static function group(): string
    {
        return 'foo';
    }
}

When resolving the class, It throws:

"0" is not a valid backing value for enum.

For the meantime, we've created a local cast but we'd love to see this supported by the package.

[rubenvanassche]

Will be fixed in the next release