How to use post steps with Jenkins pipeline on multiple agents?

Question

When using the Jenkins pipeline where each stage runs on a different agent, it is good practice to use agent none at the beginning:

pipeline {
  agent none
  stages {
    stage('Checkout') {
      agent { label 'master' }
      steps { script { currentBuild.result = 'SUCCESS' } }
    }
    stage('Build') {
      agent { label 'someagent' }
      steps { bat "exit 1" }
    }
  }
  post {
    always {
      step([$class: 'Mailer', notifyEveryUnstableBuild: true, recipients: "test@test.com", sendToIndividuals: true])
    }
  }
}

But doing this leads to Required context class hudson.FilePath is missing error message when the email should go out:

[Pipeline] { (Declarative: Post Actions)
[Pipeline] step
Required context class hudson.FilePath is missing
Perhaps you forgot to surround the code with a step that provides this, such as: node
[Pipeline] error
[Pipeline] }

When I change from agent none to agent any, it works fine.

How can I get the post step to work without using agent any?

Answer 1

wrap the step that does the mailing in a node step:

post {
  always {
    node('awesome_node_label') {
      step([$class: 'Mailer', notifyEveryUnstableBuild: true, recipients: "test@test.com", sendToIndividuals: true])
    }
  }
}