Function contains

3rd/nlohmann_json/include/nlohmann/json.hpp:4610–4613

    template < typename KeyT, typename std::enable_if <
                   !std::is_same<typename std::decay<KeyT>::type, json_pointer>::value, int >::type = 0 >
    bool contains(KeyT && key) const
    {
        return is_object() && m_value.object->find(std::forward<KeyT>(key)) != m_value.object->end();
    }

    /*!
    @brief check the existence of an element in a JSON object given a JSON pointer