NPE in io.undertow.server.Connectors.terminateResponse

2016-04-23 21:31:52,647 ERROR [io.undertow.request] (default task-96) UT005071: Undertow request failed HttpServerExchange{ POST /XXX request {Accept=[*/*], X-Requested-With=[XMLHttpRequest], Accept-Language=[en-us], Cache-Control=[no-cache],  User-Agent=[Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; rv:11.0) like Gecko], Connection=[Keep-Alive], X-Forwarded-Proto=[https], X-Forwarded-Port=[443], X-Forwarded-For=[XXX], Content-Type=[application/x-www-form-urlencoded; charset=UTF-8], Content-Length=[2014], Cookie=[JSESSIONID=Z6_twcAUmbh5EbU_cVzOr3Wj2LPj77tHJbJSs_0Z.XXX], Referer=[XXX], Host=[XXX]} response {Connection=[close], Content-Length=[0], Date=[Sun, 24 Apr 2016 01:31:52 GMT]}}: java.lang.NullPointerException
	at io.undertow.server.Connectors.terminateResponse(Connectors.java:99)
	at io.undertow.server.protocol.http.ServerFixedLengthStreamSinkConduit.channelFinished(ServerFixedLengthStreamSinkConduit.java:55)
	at io.undertow.conduits.AbstractFixedLengthStreamSinkConduit.exitFlush(AbstractFixedLengthStreamSinkConduit.java:309)
	at io.undertow.conduits.AbstractFixedLengthStreamSinkConduit.flush(AbstractFixedLengthStreamSinkConduit.java:234)
	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:478)
	at io.undertow.servlet.spec.HttpServletResponseImpl.responseDone(HttpServletResponseImpl.java:561)
	at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:332)
	at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:264)
	at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81)
	at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:175)
	at io.undertow.server.Connectors.executeRootHandler(Connectors.java:202)
	at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:792)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
	at java.lang.Thread.run(Thread.java:745)

    public boolean flush() throws IOException {
        long val = state;
        if (anyAreSet(val, FLAG_CLOSE_COMPLETE)) {
            return true;
        }
        boolean flushed = false;
        try {
            return flushed = next.flush();
        } catch (IOException e) {
            broken = true;
            throw e;
        } finally {
            exitFlush(val, flushed);
        }
    }

private void exitFlush(long oldVal, boolean flushed) {
        long newVal = oldVal;
        boolean callFinish = false;
        if ((anyAreSet(oldVal, FLAG_CLOSE_REQUESTED) || (newVal & MASK_COUNT) == 0L) && flushed) {
            newVal |= FLAG_CLOSE_COMPLETE;

            if (!anyAreSet(oldVal, FLAG_FINISHED_CALLED) && (newVal & MASK_COUNT) == 0L) {
                newVal |= FLAG_FINISHED_CALLED;
                callFinish = true;
            }
            state = newVal;
            if (callFinish) {
                channelFinished();
            }
        }
    }

    @Override
    protected void channelFinished() {
        Connectors.terminateResponse(exchange);
    }

    public static void terminateResponse(final HttpServerExchange exchange) {
        exchange.terminateResponse();
    }