Fix potential error attempting to access uninitialized property

[benno-truevault]

We want to be able to support using native types for object properties, e.g.

class MyModel {
    public int $id;
}

Without this change, the only way to support native types is to use a default value, which isn't as nice:

class ModelWithNullableDefault {
    public ?int $id = null;
}

class ModelWithZeroDefault {
    public int $id = 0;
}