End of otherwise good build with Bitbucket stacktrace

Bitbucket branch source plugin: 1.9
Bitbucket build status notifier plugin: 1.3.1
Jenkins core: 2.39
Plugins last updated 2017-01-15 evening (CET)

[Pipeline] End of Pipeline
[Bitbucket] Notifying pull request build result
[Bitbucket] Build result notified
java.lang.UnsupportedOperationException
	at java.util.Collections$UnmodifiableMap.put(Collections.java:1457)
	at groovy.lang.MetaClassImpl.setProperty(MetaClassImpl.java:2713)
	at groovy.lang.MetaClassImpl.setProperty(MetaClassImpl.java:3747)
	at org.codehaus.groovy.runtime.InvokerHelper.setProperty(InvokerHelper.java:199)
	at org.codehaus.groovy.runtime.DefaultGroovyMethods.putAt(DefaultGroovyMethods.java:272)
	at org.codehaus.groovy.runtime.dgm$508.invoke(Unknown Source)
	at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite$PojoMetaMethodSiteNoUnwrapNoCoerce.invoke(PojoMetaMethodSite.java:274)
	at org.codehaus.groovy.runtime.callsite.PojoMetaMethodSite.call(PojoMetaMethodSite.java:56)
	at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
	at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:133)
	at org.kohsuke.groovy.sandbox.impl.Checker$9.call(Checker.java:400)
	at org.kohsuke.groovy.sandbox.GroovyInterceptor.onSetArray(GroovyInterceptor.java:124)
	at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onSetArray(SandboxInterceptor.java:442)
	at org.kohsuke.groovy.sandbox.impl.Checker$9.call(Checker.java:397)
	at org.kohsuke.groovy.sandbox.impl.Checker.checkedSetArray(Checker.java:394)
	at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.setArray(SandboxInvoker.java:48)
	at com.cloudbees.groovy.cps.impl.ArrayAccessBlock.rawSet(ArrayAccessBlock.java:26)
	at WorkflowScript.run(WorkflowScript:459)
	at org.jenkinsci.plugins.pipeline.modeldefinition.when.impl.ExpressionConditionalScript.evaluate(jar:file:/opt/jenkins/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/when/impl/ExpressionConditionalScript.groovy:45)
	at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.evaluateWhen(jar:file:/opt/jenkins/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:415)
	at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.call(jar:file:/opt/jenkins/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:96)
	at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.withEnvBlock(jar:file:/opt/jenkins/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:203)
	at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.withEnvBlock(jar:file:/opt/jenkins/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:202)
	at org.jenkinsci.plugins.pipeline.modeldefinition.ModelInterpreter.call(jar:file:/opt/jenkins/plugins/pipeline-model-definition/WEB-INF/lib/pipeline-model-definition.jar!/org/jenkinsci/plugins/pipeline/modeldefinition/ModelInterpreter.groovy:95)
	at ___cps.transform___(Native Method)
	at com.cloudbees.groovy.cps.impl.PropertyishBlock$ContinuationImpl.set(PropertyishBlock.java:88)
	at com.cloudbees.groovy.cps.impl.AssignmentBlock$ContinuationImpl.assignAndDone(AssignmentBlock.java:70)
	at sun.reflect.GeneratedMethodAccessor680.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)
	at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
	at com.cloudbees.groovy.cps.impl.ConstantBlock.eval(ConstantBlock.java:21)
	at com.cloudbees.groovy.cps.Next.step(Next.java:58)
	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:163)
	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:324)
	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.access$100(CpsThreadGroup.java:78)
	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:236)
	at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:224)
	at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:63)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	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(Executors.java:511)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)
Finished: FAILURE