stdout is null when executing a command from a shared library

[Francis Pereira]

When executing commands from a shared library, stdout is always null. How do I get an handle on it ? This only happens when calling the shared library from a pipeline. If I run it in the 'Script Console' (with modification to make it execute), I get content from stdout. 

Example:

Shared library:

// CodeDeploy.groovy

class CodeDeploy {

    Script script

    def executeOnShell(String... command) {

        script.println "About to execute: " + command

        def process = new ProcessBuilder(command)

        process.redirectOutput()

        process.redirectErrorStream(true)

        def shell = process.start()

        InputStream shellIn = shell.getInputStream()

        BufferedReader reader = new BufferedReader(new InputStreamReader(shellIn))

        StringBuilder builder = new StringBuilder()

        String line = null;

        shell.waitFor()

        while ((line = reader.readLine()) != null) {

            builder.append(line);

            builder.append("\n");

        }

        script.println('Output from command: ' + builder.toString())

        int shellExitStatus = shell.exitValue();

        script.println('Exit value: ' + shellExitStatus)

        return builder.toString();

    }

}

Pipeline Usage:

//Jenkinsfile

@Library('jenkins-pipeline-libraries')

import com.wizrocket.jenkins.CodeDeploy

pipeline {

    agent any

    options {

        timestamps()

        buildDiscarder(logRotator(numToKeepStr: '9999'))

        disableConcurrentBuilds()

        timeout(time: 1, unit: 'HOURS')

    }

    stages {

        stage('lost output') {

            steps {

                script {

                    CodeDeploy cd = new CodeDeploy(script: this)

                    cd.executeOnShell('time', 'sleep', '10')

                }

            }

        }

    }

    post {

        always {

            deleteDir()

            echo 'I will always say Hello again!'

        }

    }

}

Output:

[Pipeline] }
[Pipeline] // stage
[Pipeline] timestamps
[Pipeline] {
[Pipeline] timeout
14:00:49 Timeout set to expire in 1 hr 0 min
[Pipeline] {
[Pipeline] stage
[Pipeline] { (lost output)
[Pipeline] script
[Pipeline] {
[Pipeline] echo
14:00:49 About to execute: [time, sleep, 10]
[Pipeline] echo
14:00:59 Output from command: 
[Pipeline] echo
14:00:59 Exit value: 0
[Pipeline] }
[Pipeline] // script
[Pipeline] }
[Pipeline] // stage
[Pipeline] stage
[Pipeline] { (Declarative: Post Actions)
[Pipeline] deleteDir
[Pipeline] echo
14:00:59 I will always say Hello again!
[Pipeline] }
[Pipeline] // stage
[Pipeline] }
[Pipeline] // timeout
[Pipeline] }
[Pipeline] // timestamps
[Pipeline] }
[Pipeline] // node
[Pipeline] End of Pipeline
Finished: SUCCESS