NoStaplerConstructorException for addGitLabMRComment

[avdv]

Issue

Context

• Gitlab plugin version: 1.4.0
• Gitlab version: 8.x EE (I cannot say which version, but it has the TODO feature, so I think it is at least 8.5)
• Jenkins version: 2.7.3

Problem description

I have a pipeline job, where I'm trying to submit a comment at the end of the build, I'm using the code from the migration guide:

def resultIcon = currentBuild.result == 'SUCCESS' ? ':white_check_mark:' : ':anguished:'
addGitLabMRComment comment: "$resultIcon Jenkins Build $currentBuild.result\n\nResults available at: [Jenkins [$env.JOB_NAME#$env.BUILD_NUMBER]]($env.BUILD_URL)"

I get this exception:

org.kohsuke.stapler.NoStaplerConstructorException: There's no @DataBoundConstructor on any constructor of class java.lang.String
    at org.kohsuke.stapler.ClassDescriptor.loadConstructorParamNames(ClassDescriptor.java:247)
    at org.jenkinsci.plugins.structs.describable.DescribableModel.<init>(DescribableModel.java:121)
    at org.jenkinsci.plugins.structs.describable.DescribableModel.coerce(DescribableModel.java:372)
    at org.jenkinsci.plugins.structs.describable.DescribableModel.buildArguments(DescribableModel.java:313)
    at org.jenkinsci.plugins.structs.describable.DescribableModel.instantiate(DescribableModel.java:257)
    at org.jenkinsci.plugins.workflow.steps.StepDescriptor.newInstance(StepDescriptor.java:195)
    at org.jenkinsci.plugins.workflow.cps.DSL.invokeStep(DSL.java:181)
    at org.jenkinsci.plugins.workflow.cps.DSL.invokeMethod(DSL.java:126)
    at org.jenkinsci.plugins.workflow.cps.CpsScript.invokeMethod(CpsScript.java:120)
    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 com.cloudbees.groovy.cps.sandbox.SandboxInvoker.methodCall(SandboxInvoker.java:16)
    at WorkflowScript.run(WorkflowScript:49)

I've attached a debugger and it sems the problem comes from the usage of the comment: argument passing, trying to coerce a java.util.LinkedHashMap to a String in https://github.com/jenkinsci/structs-plugin/blob/master/plugin/src/main/java/org/jenkinsci/plugins/structs/describable/DescribableModel.java#L372 -- values of the variables at that point are:

Running CpsFlowExecution[Owner[job-A/32:job-A #32]][3] print context
 context = "com.dabsquared.gitlabjenkins.workflow.AddGitLabMergeRequestCommentStep.comment"
Running CpsFlowExecution[Owner[job-A/32:job-A #32]][3] print type
 type = "class java.lang.String"
Running CpsFlowExecution[Owner[job-A/32:job-A #32]][3] print o
 o = "{comment=:white_check_mark: Jenkins Build SUCCESS

Results available at: [Jenkins [#32#32]](http://localhost:7070/jenkins/job/job-A/32/)}"

Using the following code instead works successfully:

addGitLabMRComment "$resultIcon Jenkins Build $currentBuild.result\n\nResults available at: [Jenkins [$env.JOB_NAME#$env.BUILD_NUMBER]]($env.BUILD_URL)"