message: simplifying the code for Windows compiler
diff: @@ -292,7 +292,7 @@ public: // Load/append/remove interfaces
  std::vector<T> &&data,
  size_type interval,
  bool start_from_beginning,
  - const T &null_value = get_nan<T>(),
  + const T &null_value = hmdf::get_nan<T>(),
  std::function<typename DataFrame<I, H>::size_type (
  const typename DataFrame<I, H>::IndexType &,
  const typename DataFrame<I, H>::IndexType &)> diff_func =
  