Running the following in our Pipeline script:

logstashSend failBuild: false, maxLines: 4000

Causes the following warning to appear in our Jenkins log:

Feb 07, 2018 2:51:59 PM WARNING org.jenkinsci.plugins.structs.describable.DescribableParameter uncoerce
failed to uncoerce jenkins.plugins.logstash.LogstashNotifier@17e5d3f0
java.lang.UnsupportedOperationException: no public field ‘maxLines’ (or getter method) found in class jenkins.plugins.logstash.LogstashNotifier
at org.jenkinsci.plugins.structs.describable.DescribableParameter.getValue(DescribableParameter.java:161)
at org.jenkinsci.plugins.structs.describable.DescribableParameter.inspect(DescribableParameter.java:142)
at org.jenkinsci.plugins.structs.describable.DescribableModel.uninstantiate2(DescribableModel.java:533)
at org.jenkinsci.plugins.structs.describable.DescribableModel.uninstantiate2_(DescribableModel.java:652)
at org.jenkinsci.plugins.structs.describable.DescribableParameter.uncoerce(DescribableParameter.java:196)
at org.jenkinsci.plugins.structs.describable.DescribableParameter.inspect(DescribableParameter.java:142)
at org.jenkinsci.plugins.structs.describable.DescribableModel.uninstantiate2(DescribableModel.java:533)
at org.jenkinsci.plugins.workflow.actions.ArgumentsAction.resolve(ArgumentsAction.java:305)
at org.jenkinsci.plugins.workflow.actions.ArgumentsAction.getResolvedArguments(ArgumentsAction.java:292)
at org.jenkinsci.plugins.workflow.cps.nodes.StepAtomNode.getDelegateType(StepAtomNode.java:134)
at org.jenkinsci.plugins.workflow.cps.nodes.StepAtomNode.effectiveFunctionName(StepAtomNode.java:111)
at org.jenkinsci.plugins.workflow.cps.nodes.StepAtomNode.getTypeFunctionName(StepAtomNode.java:123)
at org.jenkinsci.plugins.workflow.graph.FlowNode.getDisplayFunctionName(FlowNode.java:258)
at org.jenkinsci.plugins.workflow.support.actions.LogActionImpl$1.onNewHead(LogActionImpl.java:92)
at org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.notifyListeners(CpsFlowExecution.java:1368)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.notifyNewHead(CpsThreadGroup.java:395)
at org.jenkinsci.plugins.workflow.cps.FlowHead.setNewHead(FlowHead.java:129)
at org.jenkinsci.plugins.workflow.cps.CpsBodyExecution.addBodyEndFlowNode(CpsBodyExecution.java:405)
at org.jenkinsci.plugins.workflow.cps.CpsBodyExecution.access$800(CpsBodyExecution.java:64)
at org.jenkinsci.plugins.workflow.cps.CpsBodyExecution$SuccessAdapter.receive(CpsBodyExecution.java:363)
at com.cloudbees.groovy.cps.Outcome.resumeFrom(Outcome.java:73)
at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:166)
at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:163)
at org.codehaus.groovy.runtime.GroovyCategorySupport$ThreadCategoryInfo.use(GroovyCategorySupport.java:122)
at org.codehaus.groovy.runtime.GroovyCategorySupport.use(GroovyCategorySupport.java:261)
at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:163)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$001(SandboxContinuable.java:19)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable$1.call(SandboxContinuable.java:35)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable$1.call(SandboxContinuable.java:32)
at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.GroovySandbox.runInSandbox(GroovySandbox.java:108)
at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:32)
at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:174)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:331)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.access$200(CpsThreadGroup.java:82)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:243)
at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:231)
at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:64)
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:748)

It is non-blocking, but does spam our logs each time we run logstashSend