Nice to Madrid?

It will be a bit difficult to travel overnight from Nice to Madrid solely by rail. There used to be overnight train Milan-Barcelona via Nice, but now it's not running. Instead you can take into consideration overnighter Port Bou-Madrid (19:26-7:21), however in order to reach Port Bou on time you'll have to start from Nice in the morning, thus making it almost 24 hours to reach Madrid, which is obviously not the best solution.
Maybe a better option will be to catch evening flight from Nice to Barcelona (Vueling or EasyJet) and then either take an overnight train to Madrid or spend the night in Barcelona & take one of the multiple morning high-speed AVE trains. Or alternative will be to take an overnight bus from Nice to Barcelona (17:15-4:00 or 23:59-10:45) or even all the way to Madrid (17:15-11:15), but again spending the whole night on the bus isn't for everybody