sealed_oneof_companion_extends doesn't work for optional sealed oneof

[nodefactory-bk]

It seems the option (scalapb.message).sealed_oneof_companion_extends doesn't work for optional sealed oneofs.

This definition

message TestOf {
    option (scalapb.message).sealed_oneof_companion_extends = "Whatever";

    oneof sealed_value_optional {
        TestOfA a = 1;
    }
}

message TestOfA {
}

Generates this companion

object TestOf {
  implicit val TestOfTypeMaper....
...

Changing to non-optional sealed oneof (oneof sealed_value) generates the companion as expected:

object TestOf extends Whatever {
  case object Empty extends ....
...

/B