I've recently had to fix a compilation issue (possibly the same) by setting the MAVEN_ARGUMENTS environment variable to: --Drat.numUnapprovedLicenses=100
Incidentally: This was part of our effort to replace the standard 1.5.5 Docker image for guacamole-client with one based on Tomcat 9. It isn't hard; we did it based on the Docker setup at https://github.com/boschkundendienst and the Docker build repository provided by Guacamole (thank you, Bosch and Guacamole). I'm happy to share the results, if anyone is interested. -- Reinier Post TU Eindhoven
