Hi. I played a bit with SSE, example based on https://www.youtube.com/watch?time_continue=8&v=qQLVCgmiMgQ Code is here https://github.com/rsvoboda/rsvoboda-playground/tree/master/ee8-sample-sse For GlassFish 5 I could do just: curl -i http://localhost:8080/ee8-sample-sse/resources/beats But for WF I had to specify Accept header: curl -i -H "Accept: text/event-stream" http://localhost:8080/ee8-sample-sse/resources/beats When I used curl command which was working on GlassFish 5 I received pretty nasty NPE stacktrace. These days people are playing quite a lot with new stuff in EE8, they are using GlassFish 5 and composing their clients (Java, JavaScript, curl / libcurl ) based on this experience (who reads the spec ? when you have RI you can trust;) ). RESTEasy requirement on Accept header can be pain you_know_where for migration towards JBoss world. For sure the error message should be more user friendly and more descriptive. And I would also vote for more RI like behavior in this case. WDYT ? NPE details: Error processing request Context Path: /ee8-sample Servlet Path: /resources Path Info: /beats Query String: null Stack Trace org.jboss.resteasy.spi.UnhandledException: javax.ejb.EJBException: java.lang.NullPointerException org.jboss.resteasy.core.ExceptionHandler.handleApplicationException(ExceptionHandler.java:78) org.jboss.resteasy.core.ExceptionHandler.handleException(ExceptionHandler.java:222) org.jboss.resteasy.core.SynchronousDispatcher.writeException(SynchronousDispatcher.java:183) org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:444) org.jboss.resteasy.core.SynchronousDispatcher.lambda$invoke$1(SynchronousDispatcher.java:219) org.jboss.resteasy.core.SynchronousDispatcher.lambda$preprocess$0(SynchronousDispatcher.java:132) org.jboss.resteasy.core.interception.jaxrs.PreMatchContainerRequestContext.filter(PreMatchContainerRequestContext.java:367) org.jboss.resteasy.core.SynchronousDispatcher.preprocess(SynchronousDispatcher.java:135) org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:205) org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:227) org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56) org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51) javax.servlet.http.HttpServlet.service(HttpServlet.java:790) io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85) io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62) io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36) org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78) io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131) io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57) io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46) io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64) io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60) io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77) io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50) io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43) io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61) io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:292) io.undertow.servlet.handlers.ServletInitialHandler.access$100(ServletInitialHandler.java:81) io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:138) io.undertow.servlet.handlers.ServletInitialHandler$2.call(ServletInitialHandler.java:135) io.undertow.servlet.core.ServletRequestContextThreadSetupAction$1.call(ServletRequestContextThreadSetupAction.java:48) io.undertow.servlet.core.ContextClassLoaderSetupAction$1.call(ContextClassLoaderSetupAction.java:43) io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44) io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44) io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44) io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44) io.undertow.servlet.api.LegacyThreadSetupActionWrapper$1.call(LegacyThreadSetupActionWrapper.java:44) io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:272) io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81) io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:104) io.undertow.server.Connectors.executeRootHandler(Connectors.java:202) io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:805) java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) java.lang.Thread.run(Thread.java:748) Rostislav