message: Actually correcting what gets returned from read-only model.
diff: @@ -519,7 +519,7 @@ public:
  //the case where there's no room in the Map is woefully unhandled.
  axom_map::Node<Key, T> &ins_result = find(key);
  - return &(ins_result.first->value);
  + return ins_result.value;
  }
  /*!
  