We have setup docker-swarm-plugin which is working good. We then implemented jcasc and got the issue that after a reload the agent could not be created (it also goes to an infinite wait) and got the following error on the node:

ERROR: Unexpected error in launching an agent. This is probably a bug in Jenkins java.lang.NullPointerException at org.jenkinsci.plugins.docker.swarm.DockerSwarmCloud.getDockerSwarmApiUrl(DockerSwarmCloud.java:151) at org.jenkinsci.plugins.docker.swarm.docker.api.request.ApiRequest.<init>(ApiRequest.java:66) at org.jenkinsci.plugins.docker.swarm.docker.api.service.ServiceSpec.<init>(ServiceSpec.java:25) at org.jenkinsci.plugins.docker.swarm.DockerSwarmComputerLauncher.createCreateServiceRequest(DockerSwarmComputerLauncher.java:160) at org.jenkinsci.plugins.docker.swarm.DockerSwarmComputerLauncher.launchContainer(DockerSwarmComputerLauncher.java:119) at org.jenkinsci.plugins.docker.swarm.DockerSwarmComputerLauncher.launch(DockerSwarmComputerLauncher.java:101) at org.jenkinsci.plugins.docker.swarm.DockerSwarmComputerLauncher.launch(DockerSwarmComputerLauncher.java:56) at hudson.slaves.SlaveComputer$1.call(SlaveComputer.java:294) at jenkins.util.ContextResettingExecutorService$2.call(ContextResettingExecutorService.java:46) at jenkins.security.ImpersonatingExecutorService$2.call(ImpersonatingExecutorService.java:71) at java.util.concurrent.FutureTask.run(FutureTask.java:266) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) at java.lang.Thread.run(Thread.java:748)

Doing any arbitrary change on the docker-swarm setup in the gui made it work again. Could not find any errors in the config.xml on jenkins and the gui looks good after the reload.