Runtime error: Uninitialized attribute _s (alt/test_json_deserialization_plain_alt2.nit:22)
# JSON: {"__class": "MyClass", "i": 123, "o": null}
# Errors: 'Deserialization Error: Missing attribute `MyClass::s`', 'Deserialization Error: Missing attribute `MyClass::f`', 'Deserialization Error: Missing attribute `MyClass::a`'