In Jenkinsw pipeline, how to set a value for an environment variable when loading a shared library?

Question

I have a multi-branch pipeline that uses a Jenkinsfile to load a shared library defined in my system configuration.

@Library("my-shared-library") _
import com.company.exa.builders.BaseBuilder
import com.company.exa.builders.EdiBuilder
import hudson.model.*

buildNumbers = getBuildNumbers() // Function not shown, but it works

properties ([
  disableConcurrentBuilds(),
  [$class: 'jenkins.model.BuildDiscarderProperty',
   strategy: [$class: 'LogRotator',
              numToKeepStr: '50',
              artifactNumToKeepStr: '20']],
  parameters ([
    choiceParam(name: "VERSION_CHOICE",
                choices: buildNumbers,
                description: "Version from Builds"),
    stringParam(name: "VERSION_PASSEDIN",
                defaultValue: env.BRANCH_NAME,
                description: "Passed-in version. Note this will override VERSION_CHOICE."),
    booleanParam(name: "UPLOAD_ARTIFACTS",
                 defaultValue: false,
                 description: "Upload artifacts to file servers?"),
    choiceParam(name: "DEBUG_LEVEL",
                choices: ["0", "1", "2", "3"],
                description: "Debug level; 0=less verbose, 3=most verbose")
    ])
])

When I run it clicking Scan Multibranch Pipeline Now, I get

00:00:01.018  Loading library my-shared-library
00:00:01.019  Attempting to resolve maser from remote references...
00:00:01.019   > git --version # timeout=10
00:00:01.023   > git --version # 'git version 2.17.1'
00:00:01.023  using GIT_SSH to set credentials Jenkins Master SSH
00:00:01.028   > git ls-remote -h -- [email protected]:cfouts-kmha/kmha-infrastructure.git # timeout=10
00:00:01.546  Found match: refs/heads//master revision a1bc1e273b41c4e892d7c25814d0f2a1c261f7e5
00:00:01.546  ERROR: Checkout failed
00:00:01.546  java.lang.IllegalArgumentException: Null value not allowed as an environment variable: VERSION_PASSEDIN
00:00:01.546    at hudson.EnvVars.put(EnvVars.java:379)
00:00:01.546    at hudson.model.StringParameterValue.buildEnvironment(StringParameterValue.java:59)

...complaining that variable VERSION_PASSEDIN is null. I've tried setting the VERSION_PASSEDINvariable to just "" in the following locations to no avail...

• The multi-branch pipeline's Folder properties
• The multi-branch pipeline's parent folder properties
• In the Jenkinsfile itself
• In the System configuration global properties

Any clues on how to fix this? I have a feeling it's something obvious that I'm not seeing.

Note that if I run the job with a branch's "Build with parameters" link, the job runs fine.

Answer 1

You have a chicken-and-egg problem when trying to set default value for parameters, e.g. here:

stringParam(name: "VERSION_PASSEDIN",
                defaultValue: env.BRANCH_NAME,

To run your pipeline, Jenkins needs to figure out the value of the parameters. However, to figure out the value of the parameters, Jenkins needs to run your pipeline. See the problem?

To overcome this problem, here's what happens: Jenkins assumes the value of nothing for both VERSION_CHOICE and VERSION_PASSEDIN. In the first case, it's an empty choice; in the second, it's null.