I’m trying to use Vaadin 24.4.0.beta1 with Java 17 with Intellij IDEA. I downloaded a sample project from start.vaadin.com, it’s a chat view with multiple channels – Flow element.

I tried editing this code for a little bit. I don’t have Vaadin tools, so I checked changes in my browser. So, when I made a change to code, I pressed run ‘Application’ and when I ended, just stopped ‘Application’.

I don’t have a clue but I constantly started to receive the next Exception, when I added // todo.

ERROR 48164 --- [nio-8080-exec-2] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [com.vaadin.flow.server.ServiceException: java.lang.NullPointerException: Cannot invoke "com.vaadin.flow.server.RequestHandler.handleRequest(com.vaadin.flow.server.Vaadin session, 
com.vaadin.flow.server.VaadinRequest, com.vaadin.flow.server.VaadinResponse)" 
because "handler" is null] with root cause

java.lang.NullPointerException: Cannot invoke "com.vaadin.flow.server.RequestHandler.handleRequest(com.vaadin.flow.server.VaadinSession, com.vaadin.flow.server.VaadinRequest, com.vaadin.flow.server.VaadinResponse)" because "handler" is null
    at com.vaadin.flow.server.communication.SessionRequestHandler.handleRequest(SessionRequestHandler.java:64) ~[flow-server-24.4.0.beta1.jar:24.4.0.beta1]
    at com.vaadin.flow.server.VaadinService.handleRequest(VaadinService.java:1577) ~[flow-server-24.4.0.beta1.jar:24.4.0.beta1]
    at com.vaadin.flow.server.VaadinServlet.service(VaadinServlet.java:398) ~[flow-server-24.4.0.beta1.jar:24.4.0.beta1]
    at com.vaadin.flow.spring.SpringServlet.service(SpringServlet.java:106) ~[vaadin-spring-24.4.0.beta1.jar:na]
    at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658) ~[tomcat-embed-core-10.1.20.jar:6.0]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:206) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:150) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:653) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:419) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:313) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:277) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.springframework.web.servlet.mvc.ServletForwardingController.handleRequestInternal(ServletForwardingController.java:142) ~[spring-webmvc-6.1.6.jar:6.1.6]
    at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:178) ~[spring-webmvc-6.1.6.jar:6.1.6]
    at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:51) ~[spring-webmvc-6.1.6.jar:6.1.6]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089) ~[spring-webmvc-6.1.6.jar:6.1.6]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979) ~[spring-webmvc-6.1.6.jar:6.1.6]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014) ~[spring-webmvc-6.1.6.jar:6.1.6]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903) ~[spring-webmvc-6.1.6.jar:6.1.6]
    at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564) ~[tomcat-embed-core-10.1.20.jar:6.0]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885) ~[spring-webmvc-6.1.6.jar:6.1.6]
    at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658) ~[tomcat-embed-core-10.1.20.jar:6.0]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:206) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:150) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) ~[tomcat-embed-websocket-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:175) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:150) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-6.1.6.jar:6.1.6]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.6.jar:6.1.6]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:175) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:150) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-6.1.6.jar:6.1.6]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.6.jar:6.1.6]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:175) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:150) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-6.1.6.jar:6.1.6]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.1.6.jar:6.1.6]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:175) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:150) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:167) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:482) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:115) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:344) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:391) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:896) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1736) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-embed-core-10.1.20.jar:10.1.20]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:63) ~[tomcat-embed-core-10.1.20.jar:10.1.20]

I don’t know what to do with it except for creating new project and starting all over until again gaining the same exception?