This project is an example of the spotbugs issue #878 spotbugs/spotbugs#878. To reproduce the error this needs to be run with Java 11. In my specific case it is:
openjdk 11.0.4 2019-07-16
OpenJDK Runtime Environment (build 11.0.4+11-post-Ubuntu-1ubuntu218.04.3)
OpenJDK 64-Bit Server VM (build 11.0.4+11-post-Ubuntu-1ubuntu218.04.3, mixed mode, sharing)
run ./gradlew clean spotbugsmain on the command line