How to convert a struct that includes a pointer member to JSON with Boost Describe

In the documentation of Boost Describe, there is an example for automatic conversion of a struct to JSON (https://www.boost.org/doc/libs/1_78_0/libs/describe/doc/html/describe.html#example_to_json). However, when adding a pointer as a member of the struct, the code example does not work. I guess that the tag_invoke function needs to be modified in order to handle the pointer.

I tried the following, based on the example:

#include <boost/describe.hpp>
#include <boost/json.hpp>
#include <boost/mp11.hpp>
#include <fstream>
#include <iostream>
#include <map>
#include <type_traits>
#include <vector>

namespace app{

template <
    class T,
    class D1 = boost::describe::describe_members<
        T, boost::describe::mod_public | boost::describe::mod_protected>, //
    class D2 =
        boost::describe::describe_members<T, boost::describe::mod_private>, //
    class En = std::enable_if_t<boost::mp11::mp_empty<D2>::value &&
                                !std::is_union<T>::value> //
    >   
void tag_invoke(boost::json::value_from_tag const &, boost::json::value &v, 
                T const &t) {
  auto &obj = v.emplace_object();

  boost::mp11::mp_for_each<D1>(
      [&](auto D) { obj[D.name] = boost::json::value_from(t.*D.pointer); }); 
}

int b = 0;

struct A {
  int *i;
};

A a{&b};

}

int main() {
  std::cout << boost::json::value_from(app::a)
            << std::endl;

  return 0;
}