Nested object - java.util.NoSuchElementException: head of empty list

exception is thrown when:
```
    case class A(b: B)
    case class B(c: Option[C])
    case class C(s1: String, s2: String) 

    val msg = A(B(Some(C("ds", "xd"))))
    val bytes = msg.toPB
    val parsed = bytes.pbTo[A]
```

If you change `B` to to `case class B(c: C)` it works.
If you change `C` to `case class B(c: C)` it works.

Am I doing something wrong or is it bug?