openjdk version "21.0.11" 2026-04-21 LTS
OpenJDK Runtime Environment Corretto-21.0.11.10.1 (build 21.0.11+10-LTS)
OpenJDK 64-Bit Server VM Corretto-21.0.11.10.1 (build 21.0.11+10-LTS, mixed mode, sharing)
javac 21.0.11
Exception in thread "main" java.lang.IllegalArgumentException: return type mismatch RentalDesk.cancel
	at rental.UmlCheck.require(UmlCheck.java:27)
	at rental.UmlCheck.validate(UmlCheck.java:52)
	at rental.UmlCheck.main(UmlCheck.java:133)
