Unable to assign NULL as default value

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Version report

Jenkins and plugins versions report:

Jenkins 2.222.3
Generic Webhook Trigger 1.67
(Sorry: unable to successfully execute the instructions at ttps://www.jenkins.io/doc/book/system-administration/diagnosing-errors/#how-to-report-a-bug)

• What Operating System are you using (both controller, and any agents involved in the problem)?

Debian 4.9.168-1

Reproduction steps

• Create a Jenkinsfile with GenericTrigger code as described in the Generic Webhook Trigger documentation. E.g.

  pipeline {
  agent any
  triggers {
  GenericTrigger (
    genericVariables: [
      [ key: "pull_req", value: "\$.pullRequest.links.self[0].href", defaultValue: null ],
    ],
    token: "foo"
    printContributedVariables: true
    printPostContent: true
  )
  }
  
  stages {
  stage( "Test" ) {
    steps {
      script {
        if ( null == pull_req ) {
          echo "pull_req is null"
        }
        else {
          echo "pull_req is not null"
        }
      }
    }
  }
  }
  }

• Run this Jenkins job

Results

Expected result:

In cases where the POST content does not include the JSONPath element, I was hoping that pull_req would be a null-valued variable.

Actual result:

I am new to Groovy/scripting in general, so I will try my best to accurately describe the problem as I understand it. It looks as though null-valued variables are distinct from undeclared variables (this seems perfectly reasonable). In cases where the POST content does not include $.pullRequest.links.self[0].href, the job outputs a "No such property: pull_req for class: groovy.lang.Binding" error instead of there being a null-valued variable named pull_req

I'm new to the open source community, so I hope I'm correctly submitting a valid bug report, and have demonstrated due diligence to work around the problem (assigning a null defaultValue). Ultimately, I would like to understand/learn how to create null-valued variables when expected POST content is absent. If there is an existing mechanism within the Generic Webhook Trigger framework to deal with this, please advise -- I spent my best effort trying to find an existing solution, but could not.

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I should note: I tried:

[ key: "pull_req", value: "\$.pullRequest.links.self[0].href", defaultValue: "" ]

...but it did not have the effect of creating either a null-valued variable named pull_req, nor an empty-string-valued variable. The error, as described in the original bug report, is unchanged.

[tomasbjerre]

I tried with this pipeline:

node {
 properties([
  pipelineTriggers([
   [$class: 'GenericTrigger',
    genericVariables: [
     [
      key: 'href',
      value: '$.href'
     ]
    ],

    causeString: 'Triggered on $ref',

    token: 'abc123',
    tokenCredentialId: '',

    printContributedVariables: true,
    printPostContent: true,

    silentResponse: false
   ]
  ])
 ])

 stage("build") {
  sh '''
  echo Variables from shell:
  echo ref $href
  '''

          if (env.href) {
            echo "href is not null"
          } else {
            echo "href is null"
          }
 }
}

This will print href is null:

curl -v -H "Content-Type: application/json" -X POST -d '{  }' http://localhost:8080/jenkins/generic-webhook-trigger/invoke?token=abc123

This will print href is not null:

curl -v -H "Content-Type: application/json" -X POST -d '{ "href":"some value" }' http://localhost:8080/jenkins/generic-webhook-trigger/invoke?token=abc123

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@tomasbjerre - confirmed that I can reproduce what you described - thank you! The relevant difference appears to be referring to the variable as env.pull_req, and not just pull_req.

As an aside: this reveals something I find difficult with Jenkins scripting...there appears to be different "ways" to refer to variables...I don't know what else to call it: sometimes they are in the "global" scope, sometimes in the env scope, and apparently sometimes both.

Anyhow, this appears to be a deficiency in my understanding of the language, and not a bug. Thank you for enlightening me.