Slack notification is broken with latest plugin

[matejsp]

When having setup global slack notifier it crashes:
RunListener failed
java.lang.NoSuchMethodError: jenkins.plugins.slack.SlackNotifier$DescriptorImpl.getBotUser()Z
at org.jenkinsci.plugins.globalslack.GlobalSlackNotifier.publish(GlobalSlackNotifier.java:66)
at org.jenkinsci.plugins.globalslack.GlobalSlackNotifier.onCompleted(GlobalSlackNotifier.java:32)
at hudson.model.listeners.RunListener.fireCompleted(RunListener.java:211)
at org.jenkinsci.plugins.workflow.job.WorkflowRun.finish(WorkflowRun.java:586)
at org.jenkinsci.plugins.workflow.job.WorkflowRun.access$900(WorkflowRun.java:133)
at org.jenkinsci.plugins.workflow.job.WorkflowRun$GraphL.onNewHead(WorkflowRun.java:998)
at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.notifyListeners(CpsFlowExecution.java:1440)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$3.run(CpsThreadGroup.java:417)
at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$1.run(CpsVmExecutorService.java:35)
at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:131)
at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:59)
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
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)

[matejsp]

The crash is originating in another plugin that accesses public API of this plugin. And this plugin just broke backwards compatibility :(. It would be better to mark the method with @deprecated and after a major version bump remove it.

https://github.com/jenkinsci/global-slack-notifier-plugin/blob/master/src/main/java/org/jenkinsci/plugins/globalslack/GlobalSlackNotifier.java

[matejsp]

This specific error is fixed, but new incompatibility introduced in 2.10 is now reported in #450