Post build action in Jenkins throws NullPointerException - jenkins-pipeline

Question

I can't find what is the problem. Can anyone help to deal with the NullPointerException after post build action in Jenkins when I need to send report with the Notify.Events plugin?
post {
always {
step([$class: 'Publisher', reportFilenamePattern: '**/testng-results.xml'])
}
unstable {
step([$class: 'NotifyEventsBuilder', token: '6CGdLVTZUPWaQsz7qIGN52KRHSDuYdup', message: 'UNSTABLE TEST'])
}
failure {
step([$class: 'NotifyEventsBuilder', token: '6CGdLVTZUPWaQsz7qIGN52KRHSDuYdup', message: 'FAIL TEST'])
}
success {
step([$class: 'NotifyEventsBuilder', token: '6CGdLVTZUPWaQsz7qIGN52KRHSDuYdup', message: 'SUCCESSFUL TEST'])
}
unsuccessful {
step([$class: 'NotifyEventsBuilder', token: '6CGdLVTZUPWaQsz7qIGN52KRHSDuYdup', message: 'unsuccessful TEST'])
}
}
The result looks like this:
[Pipeline] step
Error when executing success post condition:
java.lang.NullPointerException
at events.notify.NotifyEventsService.send(NotifyEventsService.java:159)
at events.notify.NotifyEventsBuilder.perform(NotifyEventsBuilder.java:138)
at jenkins.tasks.SimpleBuildStep.perform(SimpleBuildStep.java:123)
at org.jenkinsci.plugins.workflow.steps.CoreStep$Execution.run(CoreStep.java:101)
at org.jenkinsci.plugins.workflow.steps.CoreStep$Execution.run(CoreStep.java:71)
at org.jenkinsci.plugins.workflow.steps.SynchronousNonBlockingStepExecution.lambda$start$0(SynchronousNonBlockingStepExecution.java:47)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
[Pipeline] step
Error when executing unsuccessful post condition:
java.lang.NullPointerException
at events.notify.NotifyEventsService.send(NotifyEventsService.java:159)
at events.notify.NotifyEventsBuilder.perform(NotifyEventsBuilder.java:138)
at jenkins.tasks.SimpleBuildStep.perform(SimpleBuildStep.java:123)
at org.jenkinsci.plugins.workflow.steps.CoreStep$Execution.run(CoreStep.java:101)
at org.jenkinsci.plugins.workflow.steps.CoreStep$Execution.run(CoreStep.java:71)
at org.jenkinsci.plugins.workflow.steps.SynchronousNonBlockingStepExecution.lambda$start$0(SynchronousNonBlockingStepExecution.java:47)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
[Pipeline] step
Error when executing failure post condition:
java.lang.NullPointerException
at events.notify.NotifyEventsService.send(NotifyEventsService.java:159)
at events.notify.NotifyEventsBuilder.perform(NotifyEventsBuilder.java:138)
at jenkins.tasks.SimpleBuildStep.perform(SimpleBuildStep.java:123)
at org.jenkinsci.plugins.workflow.steps.CoreStep$Execution.run(CoreStep.java:101)
at org.jenkinsci.plugins.workflow.steps.CoreStep$Execution.run(CoreStep.java:71)
at org.jenkinsci.plugins.workflow.steps.SynchronousNonBlockingStepExecution.lambda$start$0(SynchronousNonBlockingStepExecution.java:47)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
java.lang.NullPointerException
at events.notify.NotifyEventsService.send(NotifyEventsService.java:159)
at events.notify.NotifyEventsBuilder.perform(NotifyEventsBuilder.java:138)
at jenkins.tasks.SimpleBuildStep.perform(SimpleBuildStep.java:123)
at org.jenkinsci.plugins.workflow.steps.CoreStep$Execution.run(CoreStep.java:101)
at org.jenkinsci.plugins.workflow.steps.CoreStep$Execution.run(CoreStep.java:71)
at org.jenkinsci.plugins.workflow.steps.SynchronousNonBlockingStepExecution.lambda$start$0(SynchronousNonBlockingStepExecution.java:47)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)
Finished: FAILURE