Hi,

We are using Undertow in version (1.1.1.Final and 1.2.0.Beta8) as a servlet server. Between millions of requests sometimes we see in stdout this type of exception:

Exception in thread "XNIO-1 task-16" java.lang.ClassCastException: io.undertow.util.HeaderValues cannot be cast to [Lio.undertow.util.HeaderValues;
at io.undertow.util.HeaderMap.fastIterateNonEmpty(HeaderMap.java:417)
at io.undertow.server.protocol.http.HttpResponseConduit.processWrite(HttpResponseConduit.java:182)
at io.undertow.server.protocol.http.HttpResponseConduit.flush(HttpResponseConduit.java:638)
at io.undertow.conduits.AbstractFixedLengthStreamSinkConduit.flush(AbstractFixedLengthStreamSinkConduit.java:229)
at org.xnio.conduits.ConduitStreamSinkChannel.flush(ConduitStreamSinkChannel.java:162)
at io.undertow.channels.DetachableStreamSinkChannel.flush(DetachableStreamSinkChannel.java:119)
at org.xnio.channels.Channels.flushBlocking(Channels.java:63)
at io.undertow.servlet.spec.ServletOutputStreamImpl.close(ServletOutputStreamImpl.java:609)
at io.undertow.servlet.spec.HttpServletResponseImpl.closeStreamAndWriter(HttpServletResponseImpl.java:497)
at io.undertow.servlet.spec.HttpServletResponseImpl.responseDone(HttpServletResponseImpl.java:581)
at io.undertow.servlet.spec.AsyncContextImpl$3.run(AsyncContextImpl.java:320)
at io.undertow.servlet.spec.AsyncContextImpl$6.run(AsyncContextImpl.java:464)
at io.undertow.servlet.spec.AsyncContextImpl$TaskDispatchRunnable.run(AsyncContextImpl.java:581)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:724)

Undertow tries to cast io.undertow.util.HeaderValues to array of io.undertow.util.HeaderValues.