Schema validation inconsistent in case of nesting

[Dlougach]

Minimal example:

X = {
    s : string;
};

Y = {
    x : X;
};

y1 = Y {
    x = {
    };
};

y2 = Y {
    x = X {
    };
};

When evaluating y1, I get the following:

{
  "y1": {
    "x": {}
  }
}

When evaluating y2: Unknown key: 's' in composite tuple {s = <unbound>} {}

The expected behavior is that for non-required fields one can instantiate tuples without filling in those fields. Also by this logic x : required X should be different from x : X.

[Hello1024]

This behaviour is (I believe) working as intended from the language perspective.

It's the conversion to JSON that throws this error, and really it should be considering unbound variables ineligible for conversion.

I'd be happy to make a PR for this if that's the direction the project wants to go.