An object to represent any value that might come from a backend, but that we either don't know about or can't represent in this ADT.
An object to represent any value that might come from a backend, but that
we either don't know about or can't represent in this ADT. We represent it
with JS's undefined, just because no other value will ever be translated
that way.
Converts the parts of Data that it can, then stores the rest in,
effectively, Free.Pure.