It occurs to me quite regularly:

I have servlet, construct some GET URL and find bug. So I fix it, redeploy my war application and press reload in firefox. But WildFly fails with NPE. If I reload the page again, then it works.

22:21:59,888 ERROR [io.undertow.request] (default I/O-3) Blocking request failed HttpServerExchange

: java.lang.NullPointerException
at org.jboss.weld.context.http.HttpConversationContextImpl.getRequestAttribute(HttpConversationContextImpl.java:47)
at org.jboss.weld.context.http.HttpConversationContextImpl.getRequestAttribute(HttpConversationContextImpl.java:13)
at org.jboss.weld.context.AbstractConversationContext.copyConversationIdGeneratorAndConversationsToSession(AbstractConversationContext.java:177)
at org.jboss.weld.context.AbstractConversationContext.sessionCreated(AbstractConversationContext.java:185)
at org.jboss.weld.servlet.ConversationContextActivator.sessionCreated(ConversationContextActivator.java:187)
at org.jboss.weld.servlet.HttpContextLifecycle.sessionCreated(HttpContextLifecycle.java:122)
at org.jboss.weld.servlet.WeldInitialListener.sessionCreated(WeldInitialListener.java:107)
at io.undertow.servlet.core.ApplicationListeners.sessionCreated(ApplicationListeners.java:256)
at io.undertow.servlet.core.SessionListenerBridge.sessionCreated(SessionListenerBridge.java:36)
at io.undertow.server.session.SessionListeners.sessionCreated(SessionListeners.java:32)
at io.undertow.server.session.InMemorySessionManager.createSession(InMemorySessionManager.java:121)
at io.undertow.servlet.spec.ServletContextImpl.getSession(ServletContextImpl.java:677)
at io.undertow.servlet.spec.ServletContextImpl.getSession(ServletContextImpl.java:691)
at io.undertow.servlet.handlers.SessionRestoringHandler.handleRequest(SessionRestoringHandler.java:110)
at io.undertow.server.handlers.PathHandler.handleRequest(PathHandler.java:56)
at io.undertow.server.handlers.NameVirtualHostHandler.handleRequest(NameVirtualHostHandler.java:53)
at io.undertow.server.handlers.error.SimpleErrorPageHandler.handleRequest(SimpleErrorPageHandler.java:76)
at io.undertow.server.handlers.CanonicalPathHandler.handleRequest(CanonicalPathHandler.java:43)
at io.undertow.server.handlers.ChannelUpgradeHandler.handleRequest(ChannelUpgradeHandler.java:158)
at io.undertow.server.Connectors.executeRootHandler(Connectors.java:164)
at io.undertow.server.protocol.http.HttpReadListener.handleEvent(HttpReadListener.java:142)
at io.undertow.server.protocol.http.HttpOpenListener.handleEvent(HttpOpenListener.java:69)
at io.undertow.server.protocol.http.HttpOpenListener.handleEvent(HttpOpenListener.java:38)
at org.xnio.ChannelListeners.invokeChannelListener(ChannelListeners.java:92) [xnio-api-3.2.0.Beta4.jar:3.2.0.Beta4]
at org.xnio.ChannelListeners$10.handleEvent(ChannelListeners.java:291) [xnio-api-3.2.0.Beta4.jar:3.2.0.Beta4]
at org.xnio.ChannelListeners$10.handleEvent(ChannelListeners.java:286) [xnio-api-3.2.0.Beta4.jar:3.2.0.Beta4]
at org.xnio.ChannelListeners.invokeChannelListener(ChannelListeners.java:92) [xnio-api-3.2.0.Beta4.jar:3.2.0.Beta4]
at org.xnio.nio.NioTcpServerHandle.handleReady(NioTcpServerHandle.java:53) [xnio-nio-3.2.0.Beta4.jar:3.2.0.Beta4]
at org.xnio.nio.WorkerThread.run(WorkerThread.java:531) [xnio-nio-3.2.0.Beta4.jar:3.2.0.Beta4]