Function is_null

Source/external/json.hpp:20480–20483

@brief return whether value is null @sa https://json.nlohmann.me/api/basic_json/is_null/

	/// @brief return whether value is null
	/// @sa https://json.nlohmann.me/api/basic_json/is_null/
	constexpr bool is_null() const noexcept
	{
		return m_type == value_t::null;
	}

	/// @brief return whether value is a boolean
	/// @sa https://json.nlohmann.me/api/basic_json/is_boolean/