If the Str _unmarshal gets a Nil it wasn't returning anything
If the Str _unmarshal gets a Nil it wasn't returning anything

Consequently it was implicitly returning an empty Slip which
would then cause the initialisation of the Str attribute to
fail with a type constraint failure. Returning a Str type
object is sufficient to fix this.

tadzik/JSON-Unmarshal,tadzik/JSON-Unmarshal