java.lang.AssertionError: null in ConnectorTracker

Hi,

we check regularly the logs of our customers and an AssertionError occures very often since we updated the vaadin version from 8.16.1 to 8.17.0.
Stacktrace:

java.lang.AssertionError: null at com.vaadin.ui.ConnectorTracker.getDiffState(ConnectorTracker.java:700) at com.vaadin.server.LegacyCommunicationManager.encodeState(LegacyCommunicationManager.java:96) at com.vaadin.server.AbstractClientConnector.encodeState(AbstractClientConnector.java:292) at com.vaadin.server.communication.SharedStateWriter.write(SharedStateWriter.java:67) at com.vaadin.server.communication.UidlWriter.write(UidlWriter.java:176) at com.vaadin.server.communication.UidlRequestHandler.writeUidl(UidlRequestHandler.java:125) at com.vaadin.server.communication.UidlRequestHandler.synchronizedHandleRequest(UidlRequestHandler.java:93) at com.vaadin.server.SynchronizedRequestHandler.handleRequest(SynchronizedRequestHandler.java:40) at com.vaadin.server.VaadinService.handleRequest(VaadinService.java:1669) at com.vaadin.server.VaadinServlet.service(VaadinServlet.java:464) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:239) at net.bull.javamelody.MonitoringFilter.doFilter(MonitoringFilter.java:215) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)

Can you explain it what does it mean and when/why does it happen?

Kind regards
Noemi (FOCONIS AG)

Start with ConnectorTracker.getDiffState at ConnectorTracker.java:700 and follow the call chain through LegacyCommunicationManager.encodeState, AbstractClientConnector.encodeState, SharedStateWriter.write, and UidlWriter.write. Compare behavior between Vaadin 8.16.1 and 8.17.0 using the reported stack trace; done means identifying the triggering state and documenting when and why the assertion occurs.