message: Fix return_type_ string while printing a DEX method
diff: @@ -156,9 +156,10 @@ std::ostream& operator<<(std::ostream& os, const Method& method) {
  if (!flags_str.empty()) {
  os << flags_str << " ";
  }
  - os << proto->return_type()
  - << " "
  - << pretty_cls_name << "->" << method.name();
  + if (const auto* t = proto->return_type()) {
  + os << *t << " ";
  + }
  + os << pretty_cls_name << "->" << method.name();
  os << "(";
  for (size_t i = 0; i < ps.size(); ++i) {
  