message: Fix sum type unit test
diff: @@ -85,11 +85,11 @@ public:
  }
  private:
  - inline union_type& data() {
  + inline union_type& get_data() {
  return *this;
  }
  - inline const union_type& data() const {
  + inline const union_type& get_data() const {
  return *this;
  }
  