This bug was originally marked as duplicate of bug 241006, that is already resolved. This bug is still valid, so this seems to be another bug, but it might be related.

Build: NetBeans IDE Dev (Build 201503040001)
VM: Java HotSpot(TM) Client VM, 25.40-b25, Java(TM) SE Runtime Environment, 1.8.0_40-b25
OS: Linux

User Comments:
NukemBy: During copy/paste of java code

skygo: using code completion within try with resources block

akobberup: Invoking code completion

gtzabari: Hit CTRL+P on constructor argument.

markiewb: Code completion -> Exception

Chiana: Was just editing some code, removed a part that was not correct and started typing the correct part.

gtzabari: Saved file. Exception thrown.

GUEST: Coding in a newjersey findall_xml client method

vriha: just using code completion in Maven Web project in Java file

Chiana: Was continuing to type after report #206993, this occured when CC was invoked again (after next dot typed)




Stacktrace: 
java.lang.AssertionError: Wrong diagnostic handler: com.sun.tools.javac.util.Log$DiscardDiagnosticHandler@1c1d7de
Thread dump:
WebSocketServer
	sun.nio.ch.EPollArrayWrapper.epollWait(Native Method)
	sun.nio.ch.EPollArrayWrapper.poll(EPollArrayWrapper.java:269)
	sun.nio.ch.EPollSelectorImpl.doSelect(EPollSelectorImpl.java:79)
	sun.nio.ch.SelectorImpl.lockAndDoSelect(SelectorImpl.java:86)
	sun.nio.ch.SelectorImpl.select(SelectorImpl.java:97)
	sun.nio.ch.SelectorImpl.select(SelectorImpl.java:101)
	org.netbeans.modules.netserver.SocketFramework.doRun(SocketFramework.java:121)
	org.netbeans.modules.netserver.SocketServer.run(SocketServer.java:77)
	org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1425)
	org.netbeans.modules.openide.util.GlobalLookup.execute(GlobalLookup.java:59)
	org.openide.util.lookup.Lookups.executeWith(Lookups.java:294)
	org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2038)
Deadlock Detector
	java.lang.Thread.sleep(Native Method)
	org.netbeans.modules.deadl
   at com.sun.tools.javac.util.Assert.error(Assert.java:133)
   at com.sun.tools.javac.util.Assert.check(Assert.java:86)
   at com.sun.tools.javac.util.Log.popDiagnosticHandler(Log.java:481)
   at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.showDiagnostics(JavacProcessingEnvironment.java:1075)
   at com.sun.tools.javac.processing.JavacProcessingEnvironment.doProcessing(JavacProcessingEnvironment.java:1131)
   at com.sun.tools.javac.main.JavaCompiler.processAnnotations(JavaCompiler.java:1230)