Funky value classes unwrap does not work

[jerrevanveluw]

given:

@JvmInline
value class FirstName private constructor(
override val value: String,
) : Value {
override fun toString() = value

companion object {
    operator fun invoke(s: String) =
        either {
            ensure(s.isNotBlank()) { FirstNameError.Empty }
            FirstName(s.trim())
        }
}

}

and TO:
data class UserDto(
val firstName: String,
)

and FROM:

data class User(
val firstName: FirstName,
)

the function:
fun User.produce(): UserDto = mapper {}

compiles, but is not filled and the test fails: expected: but was:<>