Function from_json

extern/json/json.hpp:4597–4604

template<typename BasicJsonType>
inline void from_json(const BasicJsonType& j, typename std::nullptr_t& n)
{
    if (JSON_HEDLEY_UNLIKELY(!j.is_null()))
    {
        JSON_THROW(type_error::create(302, concat("type must be null, but is ", j.type_name()), &j));
    }
    n = nullptr;
}

// overloads for basic_json template parameters
template < typename BasicJsonType, typename ArithmeticType,