Comment imprimer un groovy variable?

J'ai le code suivant à l'intérieur d'un Jenkins pipeline:

stage ('Question') {
    try {
        timeout(time: 1, unit: 'MINUTES') {
            userInput = input message: 'Choose server to publish to:', ok: '', parameters: [
                [$class: 'hudson.model.ChoiceParameterDefinition', choices: 'pc-ensureint\nother-server', description: 'Choose server to publish to:', name: 'server']
        ] 
      }
    } catch (err) {
        userInput = [server: 'pc-ensureint'] //if an error is caught set this value
    }
}

node () {
    println ${server}
}

Je suis en train de résoudre un problème avec le "serveur" de la variable qui est définie dans la "ChoiceParameterDefinition".

Quand je lance la compilation, j'obtiens l'erreur suivante:

java.lang.NoSuchMethodError: No such DSL method '$' found among steps [AddInteractivePromotion, ArtifactoryGradleBuild, ArtifactoryMavenBuild, ConanAddRemote, ConanAddUser, InitConanClient, MavenDescriptorStep, RunConanCommand, ansiblePlaybook, archive, artifactoryDownload, artifactoryPromoteBuild, artifactoryUpload, bat, build, catchError, checkout, collectEnv, deleteDir, dir, dockerFingerprintFrom, dockerFingerprintRun, dockerPullStep, dockerPushStep, echo, emailext, emailextrecipients, envVarsForTool, error, fileExists, getArtifactoryServer, getContext, getDatabaseConnection, git, input, isUnix, library, libraryResource, load, mail, milestone, newArtifactoryServer, newBuildInfo, newGradleBuild, newMavenBuild, node, parallel, properties, publishBuildInfo, pwd, readFile, readTrusted, resolveScm, retry, script, sh, sleep, sql, stage, stash, step, svn, timeout, timestamps, tool, unarchive, unstash, validateDeclarativePipeline, waitForQualityGate, waitUntil, withContext, withCredentials, withDockerContainer, withDockerRegistry, withDockerServer, withEnv, wrap, writeFile, ws, xrayScanBuild] or symbols [all, allOf, always, ant, antFromApache, antOutcome, antTarget, any, anyOf, apiToken, architecture, archiveArtifacts, artifactManager, batchFile, booleanParam, branch, buildButton, buildDiscarder, caseInsensitive, caseSensitive, choice, choiceParam, cleanWs, clock, cloud, command, configFile, configFileProvider, cron, crumb, defaultView, demand, disableConcurrentBuilds, docker, dockerfile, downloadSettings, downstream, dumb, envVars, environment, expression, file, fileParam, filePath, fingerprint, frameOptions, freeStyle, freeStyleJob, git, github, githubPush, gradle, hyperlink, hyperlinkToModels, installSource, jdk, jdkInstaller, jgit, jgitapache, jnlp, jobName, junit, label, lastDuration, lastFailure, lastGrantedAuthorities, lastStable, lastSuccess, legacy, legacySCM, list, local, location, logRotator, loggedInUsersCanDoAnything, masterBuild, maven, maven3Mojos, mavenErrors, mavenMojos, mavenWarnings, modernSCM, msbuild, msbuildError, msbuildWarning, myView, node, nodeProperties, nonStoredPasswordParam, none, not, overrideIndexTriggers, paneStatus, parameters, password, pattern, pipeline-model, pipelineTriggers, plainText, plugin, pollSCM, projectNamingStrategy, proxy, queueItemAuthenticator, quietPeriod, remotingCLI, run, runParam, schedule, scmRetryCount, search, security, shell, skipDefaultCheckout, skipStagesAfterUnstable, slave, stackTrace, standard, status, string, stringParam, swapSpace, text, textParam, tmpSpace, toolLocation, unsecured, upstream, usernameColonPassword, usernamePassword, viewsTabBar, weather, withSonarQubeEnv, zfs, zip] or globals [Artifactory, currentBuild, docker, env, params, pipeline, scm]
at org.jenkinsci.plugins.workflow.cps.DSL.invokeMethod(DSL.java:149)
at org.jenkinsci.plugins.workflow.cps.CpsScript.invokeMethod(CpsScript.java:108)
at groovy.lang.GroovyObject$invokeMethod.call(Unknown Source)
at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:151)
at org.kohsuke.groovy.sandbox.GroovyInterceptor.onMethodCall(GroovyInterceptor.java:21)
at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onMethodCall(SandboxInterceptor.java:115)
at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:149)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:146)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:123)
at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:123)
at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.methodCall(SandboxInvoker.java:16)
at WorkflowScript.run(WorkflowScript:16)
at ___cps.transform___(Native Method)
at com.cloudbees.groovy.cps.impl.ContinuationGroup.methodCall(ContinuationGroup.java:57)
at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:109)
at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:82)
at sun.reflect.GeneratedMethodAccessor637.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
at com.cloudbees.groovy.cps.impl.ClosureBlock.eval(ClosureBlock.java:46)
at com.cloudbees.groovy.cps.Next.step(Next.java:74)
at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:154)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$001(SandboxContinuable.java:18)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable$1.call(SandboxContinuable.java:33)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable$1.call(SandboxContinuable.java:30)
at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.GroovySandbox.runInSandbox(GroovySandbox.java:108)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:30)
at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:165)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:330)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.access$100(CpsThreadGroup.java:82)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:242)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:230)
at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:64)
at java.util.concurrent.FutureTask.run(Unknown Source)
at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:112)
at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
at java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
at java.util.concurrent.FutureTask.run(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
Finished: FAILURE

Autant que je sache, le "serveur" est un groovy variable et donc je suis censé être en mesure d'accéder à l'aide de ${}.

J'ai donc essayé:

echo ${server}
print ${server}
println ${server}
println "${server}"

Mais peu importe ce que j'essaie, je reçois cette erreur.

Une idée de ce que je fais mal?