message: hammer: using emplace
diff: @@ -2967,7 +2967,7 @@ class parser
  if (keep and keep_tag and not value.is_discarded())
  {
  - result.m_value.object->operator[](std::move(key)) = std::move(value);
  + result.m_value.object->emplace(std::move(key), std::move(value));
  }
  // comma -> next value
  