Jenkins Pipeline external script returning a null value

Question

My question is similar to this one about how to load an external groovy script, and then calling a method from it in a different groovy script. So far I have been able to get methods that don't return a value to work but I am having trouble getting a returned value into a variable that is called.

For example, the following pipeline code works but gives a value of null for $build_user when I run the Jenkins pipeline. It doesn't actually return what I expect it to and I don't know why.

node {
    stage('test') {
        def tools = load "/var/lib/jenkins/workflow-libs/vars/tools.groovy"
        build_user = tools.get_user()
        echo "build_user: $build_user"
    }
}

Here is what the relevant tools.groovy looks like.

def exampleMethod() {
    // Do stuff
}

// Try to get a build username
def get_user() {

    try {
        wrap([$class: 'BuildUser']) {
            // Set up our variables
            fallback_user = 'GitHub'
            github_user = BUILD_USER
            commit_author = 'Test1'

            // Try to use Jenkins build user first
            if (github_user) {
                echo "using github_user: $github_user"
                return github_user
            }
            // Otherwise try to use commit author
            else if (commit_author) {
                echo "using commit_author: $commit_author"
                return commit_author
            }
            // Otherwise username is blank so we use the default fallback
            else {
                echo "using fallback: $fallback_user"
                return fallback_user
            }
        }
    }
    catch (err) {
        // Ignore errors
    }

    echo "Done."
}

return this

Here is the full Jenkins output for the above code.

Started by user XXX
[Pipeline] node
Running on master in /var/lib/jenkins/workspace/test
[Pipeline] {
[Pipeline] stage
[Pipeline] { (test)
[Pipeline] load
[Pipeline] { (/var/lib/jenkins/workflow-libs/vars/tools.groovy)
[Pipeline] }
[Pipeline] // load
[Pipeline] wrap
[Pipeline] {
[Pipeline] echo
using github_user: XXX
[Pipeline] }
[Pipeline] // wrap
[Pipeline] echo
Done.
[Pipeline] echo
build_user: null
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Finished: SUCCESS

---

The above method doesn't work at all if I remove return this at the end and throws the following error in Jenkins.

java.lang.NullPointerException: Cannot invoke method get_user() on null object ...

What am I doing wrong? I suspect that I'm missing something easy but I'm not great with Groovy, so I'm not sure what it could be.

Answer 1

You have to end your tools.groovy with return this .
See the answer on this question How do you load a groovy file and execute it

Answer 2

your function get_user() returns nothing.

the return(s) inside wrap([$class: 'BuildUser']) {...} do return from wrap class and not from your function.