message: Make initialization options parsing less crashy if null is passed instead of undefined/nothing.
  See issue
diff: @@ -40,6 +40,9 @@ class JsonReader : public Reader {
  }
  void DoMember(const char* name, std::function<void(Reader&)> fn) override {
  + if (m_->GetType() != rapidjson::Type::kObjectType)
  + return; // FIXME: signal an error that object was not deserialized correctly?
  +
  auto it = m_->FindMember(name);
  if (it != m_->MemberEnd()) {
  JsonReader sub(&it->value);
  