I'm not familiar with this particular bike but many from this era have a vacuum operated fuel valve.
These usually have a PRIME or PRI setting to force fuel to flow even without the engine running to pull the vacuum and open the fuel valve.
What happens is that you run out of fuel and the carb bowls are empty and there is nothing to start the engine. Normally there is enough fuel in the bowls to get the engine started and then the vacuum valve will open up and let more fuel in.
Check your fuel valve for the PRIME position and turn it that way and wait about a minute, then try to start the bike normally. You may need to add some choke.
If it started, turn the fuel valve back to the "NORMAL" position so that the fuel delivery will stop when your shut off the engine.
If it doesn't start then there may be a problem with the fuel valve or tubing and you'll want to investigate that further. The PRI position usually has a separate and LOWER fuel pickup screen in the tank and that can become clogged with debris over time. This is an older bike and there may be bits of dirt or rust or other gunk that has accumulated. If needed you may need to drain the tank and remove the fuel valve assembly and clean it and/or replace the screens.