Yes, of course there should be two filters. And yes, it will work on one, however you will not have a visible water trap. The first (missing) filter in line from the tank should have the glass bowl under it so that you check and drain it as required. In the UK the later 500 series tractors pair of filters were replaced with one larger capacity one with a drain tap in the lower cup.
No matter how careful you are you will always get a build-up of water over time. Filling the tank at the end of the day's work, not the beginning, will help to reduce water forming from condensation. It would be advisable to refit the missing filter asap. There should be secondhand ones available from breakers although new would be better in terms of possible aluminium thread damage through past pipe disconnections.
DavidP, South Wales