data class Foo(
   val bar : Baz
)
data class Baz(
   val smth : String
   val zzz : String?
)

zzz

zzz

data class Foo(
    val bar : Baz<String>
)
data class Baz<T : String?>(
    val smth : String,
    val zzz : T
)

data class Foo(
   override val bar : Baz
) : InterfaceWithBarFromLibrary
data class BazFromLibrary(
   val smth : String
   val zzz : String?
)