Jenkins Workflow: Unable to implement trait in Shared Library - jenkins

Question

Setup
Let's assume I have the following configuration on my Jenkins Shared Library:
vars/
utils.groovy
src/
com.my.corp.utils/
tools/
Utilities.groovy
helpers/
Workflow.groovy
Workflow.groovy
package com.my.corp.utils.helpers
// import org.jenkinsci.plugins.workflow.cps.CpsScript
trait Workflow
{
def workflow
}
Utitities.groovy
package com.my.corp.utils.tools
import com.my.corp.utils.helpers.Workflow
// import org.jenkinsci.plugins.workflow.cps.CpsScript
class Utilities implements Serializable, Workflow
{
def x = 5
def y = 10
def echo(Map args)
{
this.workflow.sh """echo 'args: ${args}'"""
this.workflow.sh """echo 'args.inspect(): ${args.inspect()}'"""
this.workflow.sh """echo 'this.steps: ${this.workflow}'"""
this.workflow.echo message: args.inspect()
this.workflow.sh """echo "${this.workflow.class.getName()}; args: ${args}\""""
}
}
utils.groovy
import com.my.corp.utils.tools.Utilities
def call(Map params)
{
this.echo "${this}"
params.put('workflow', this)
new Utilities(params).echo(params)
}
The Problem
When, in the main pipeline, I call utils x: 1, y: 2,
the following error appears:
org.jenkinsci.plugins.workflow.cps.CpsCompilationErrorsException: startup failed
Full Trace
Long Java stacktrace warning!
14:56:21 org.jenkinsci.plugins.workflow.cps.CpsCompilationErrorsException: startup failed:
14:56:21 file:/var/lib/jenkins/jobs/Sandbox-Pipeline/builds/74/libs/245eaa38d10b90e40a75ee9676c50aa097d56330cf312d54476ed05f2c731cfa/src/com/my/corp/utils/tools/Utilities.groovy: -1: Unsupported array expression for CPS transformation in this context # line -1, column -1.
14:56:21 file:/var/lib/jenkins/jobs/Sandbox-Pipeline/builds/74/libs/245eaa38d10b90e40a75ee9676c50aa097d56330cf312d54476ed05f2c731cfa/src/com/my/corp/utils/tools/Utilities.groovy: -1: Unsupported array expression for CPS transformation in this context # line -1, column -1.
14:56:21 2 errors
14:56:21
14:56:21 at org.codehaus.groovy.control.ErrorCollector.failIfErrors(ErrorCollector.java:309)
14:56:21 at org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:1107)
14:56:21 at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:624)
14:56:21 at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:602)
14:56:21 at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:579)
14:56:21 at groovy.lang.GroovyClassLoader.doParseClass(GroovyClassLoader.java:323)
14:56:21 at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:293)
14:56:21 at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:279)
14:56:21 at groovy.lang.GroovyClassLoader.recompile(GroovyClassLoader.java:786)
14:56:21 at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:743)
14:56:21 at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:812)
14:56:21 at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:576)
14:56:21 at org.jenkinsci.plugins.workflow.cps.CpsGroovyShell$TimingLoader.loadClass(CpsGroovyShell.java:170)
14:56:21 at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:576)
14:56:21 at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:702)
14:56:21 at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:812)
14:56:21 at groovy.lang.GroovyClassLoader.loadClass(GroovyClassLoader.java:800)
14:56:21 at org.jenkinsci.plugins.workflow.cps.global.UserDefinedGlobalVariable.getValue(UserDefinedGlobalVariable.java:52)
14:56:21 at org.jenkinsci.plugins.workflow.cps.CpsScript.invokeMethod(CpsScript.java:115)
14:56:21 at jdk.internal.reflect.GeneratedMethodAccessor7858.invoke(Unknown Source)
14:56:21 at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
14:56:21 at java.base/java.lang.reflect.Method.invoke(Method.java:566)
14:56:21 at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:98)
14:56:21 at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
14:56:21 at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1225)
14:56:21 at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1034)
14:56:21 at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:41)
14:56:21 at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:47)
14:56:21 at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:116)
14:56:21 at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:163)
14:56:21 at org.kohsuke.groovy.sandbox.GroovyInterceptor.onMethodCall(GroovyInterceptor.java:23)
14:56:21 at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onMethodCall(SandboxInterceptor.java:158)
14:56:21 at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:161)
14:56:21 at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:165)
14:56:21 at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:135)
14:56:21 at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:135)
14:56:21 at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:135)
14:56:21 at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.methodCall(SandboxInvoker.java:17)
14:56:21 at WorkflowScript.run(WorkflowScript:18)
14:56:21 at ___cps.transform___(Native Method)
14:56:21 at com.cloudbees.groovy.cps.impl.ContinuationGroup.methodCall(ContinuationGroup.java:86)
14:56:21 at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:113)
14:56:21 at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:83)
14:56:21 at jdk.internal.reflect.GeneratedMethodAccessor741.invoke(Unknown Source)
14:56:21 at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
14:56:21 at java.base/java.lang.reflect.Method.invoke(Method.java:566)
14:56:21 at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
14:56:21 at com.cloudbees.groovy.cps.impl.CollectionLiteralBlock$ContinuationImpl.dispatch(CollectionLiteralBlock.java:55)
14:56:21 at com.cloudbees.groovy.cps.impl.CollectionLiteralBlock$ContinuationImpl.item(CollectionLiteralBlock.java:45)
14:56:21 at jdk.internal.reflect.GeneratedMethodAccessor744.invoke(Unknown Source)
14:56:21 at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
14:56:21 at java.base/java.lang.reflect.Method.invoke(Method.java:566)
14:56:21 at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
14:56:21 at com.cloudbees.groovy.cps.impl.ConstantBlock.eval(ConstantBlock.java:21)
14:56:21 at com.cloudbees.groovy.cps.Next.step(Next.java:83)
14:56:21 at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:174)
14:56:21 at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:163)
14:56:21 at org.codehaus.groovy.runtime.GroovyCategorySupport$ThreadCategoryInfo.use(GroovyCategorySupport.java:136)
14:56:21 at org.codehaus.groovy.runtime.GroovyCategorySupport.use(GroovyCategorySupport.java:275)
14:56:21 at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:163)
14:56:21 at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$001(SandboxContinuable.java:18)
14:56:21 at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:51)
14:56:21 at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:187)
14:56:21 at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:420)
14:56:21 at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.access$400(CpsThreadGroup.java:95)
14:56:21 at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:330)
14:56:21 at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:294)
14:56:21 at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:67)
14:56:21 at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
14:56:21 at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:139)
14:56:21 at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
14:56:21 at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:68)
14:56:21 at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
14:56:21 at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
14:56:21 at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
14:56:21 at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
14:56:21 at java.base/java.lang.Thread.run(Thread.java:829)
However
However, if I change the Workflow to be an abstract class instead of trait, and use extends Workflow implements Serializible instead of implements Workflow, Serializible in the Utilities definition, everything works fine!
Furthermore, when I run the code above (with traits) in Groovy online executor, it works well too.