Function back

include/behaviortree_cpp/contrib/json.hpp:21710–21715

@brief access the last element @sa https://json.nlohmann.me/api/basic_json/back/

    /// @brief access the last element
    /// @sa https://json.nlohmann.me/api/basic_json/back/
    reference back()
    {
        auto tmp = end();
        --tmp;
        return *tmp;
    }

    /// @brief access the last element
    /// @sa https://json.nlohmann.me/api/basic_json/back/