To whom it might be of interest of:
During boot I received the follwoing error message:
2021-12-29 12:33:34.113 [ERROR] [internal.JSONResponseExceptionMapper] - Unexpected exception occurred while processing REST request.
java.lang.NullPointerException: null
at java.util.concurrent.CopyOnWriteArrayList.addAllAbsent(CopyOnWriteArrayList.java:691) ~[?:?]
at java.util.concurrent.CopyOnWriteArraySet.addAll(CopyOnWriteArraySet.java:330) ~[?:?]
at org.openhab.core.io.rest.sse.internal.SseSinkItemInfo.updateTrackedItems(SseSinkItemInfo.java:49) ~[?:?]
at org.openhab.core.io.rest.sse.SseResource.updateTrackedItems(SseResource.java:218) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:?]
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
at java.lang.reflect.Method.invoke(Method.java:566) ~[?:?]
at org.apache.cxf.service.invoker.AbstractInvoker.performInvocation(AbstractInvoker.java:179) ~[bundleFile:3.4.5]
at org.apache.cxf.service.invoker.AbstractInvoker.invoke(AbstractInvoker.java:96) ~[bundleFile:3.4.5]
at org.apache.cxf.jaxrs.JAXRSInvoker.invoke(JAXRSInvoker.java:201) ~[bundleFile:3.4.5]
at org.apache.cxf.jaxrs.JAXRSInvoker.invoke(JAXRSInvoker.java:104) ~[bundleFile:3.4.5]
at org.apache.cxf.interceptor.ServiceInvokerInterceptor$1.run(ServiceInvokerInterceptor.java:59) ~[bundleFile:3.4.5]
at org.apache.cxf.interceptor.ServiceInvokerInterceptor.handleMessage(ServiceInvokerInterceptor.java:96) ~[bundleFile:3.4.5]
at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:308) ~[bundleFile:3.4.5]
at org.apache.cxf.transport.ChainInitiationObserver.onMessage(ChainInitiationObserver.java:121) ~[bundleFile:3.4.5]
at org.apache.cxf.transport.http.AbstractHTTPDestination.invoke(AbstractHTTPDestination.java:265) ~[bundleFile:3.4.5]
at org.apache.cxf.transport.servlet.ServletController.invokeDestination(ServletController.java:234) ~[bundleFile:3.4.5]
at org.apache.cxf.transport.servlet.ServletController.invoke(ServletController.java:208) ~[bundleFile:3.4.5]
at org.apache.cxf.transport.servlet.ServletController.invoke(ServletController.java:160) ~[bundleFile:3.4.5]
at org.apache.cxf.transport.servlet.CXFNonSpringServlet.invoke(CXFNonSpringServlet.java:225) ~[bundleFile:3.4.5]
at org.apache.cxf.transport.servlet.AbstractHTTPServlet.handleRequest(AbstractHTTPServlet.java:298) ~[bundleFile:3.4.5]
at org.apache.cxf.transport.servlet.AbstractHTTPServlet.doPost(AbstractHTTPServlet.java:217) ~[bundleFile:3.4.5]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:707) ~[bundleFile:3.1.0]
at org.apache.cxf.transport.servlet.AbstractHTTPServlet.service(AbstractHTTPServlet.java:273) ~[bundleFile:3.4.5]
at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:799) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:550) ~[bundleFile:9.4.43.v20210629]
at org.ops4j.pax.web.service.jetty.internal.HttpServiceServletHandler.doHandle(HttpServiceServletHandler.java:71) ~[bundleFile:?]
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:143) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.security.SecurityHandler.handle(SecurityHandler.java:602) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:127) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:235) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:1624) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.handler.ScopedHandler.nextHandle(ScopedHandler.java:233) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1434) ~[bundleFile:9.4.43.v20210629]
at org.ops4j.pax.web.service.jetty.internal.HttpServiceContext.doHandle(HttpServiceContext.java:294) ~[bundleFile:?]
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:188) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:501) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:1594) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.handler.ScopedHandler.nextScope(ScopedHandler.java:186) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1349) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141) ~[bundleFile:9.4.43.v20210629]
at org.ops4j.pax.web.service.jetty.internal.JettyServerHandlerCollection.handle(JettyServerHandlerCollection.java:82) ~[bundleFile:?]
at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:127) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.Server.handle(Server.java:516) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.HttpChannel.lambda$handle$1(HttpChannel.java:388) ~[bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.HttpChannel.dispatch(HttpChannel.java:633) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:380) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.HttpChannelOverHttp.earlyEOF(HttpChannelOverHttp.java:237) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.http.HttpParser.parseNext(HttpParser.java:1614) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.HttpConnection.parseRequestBuffer(HttpConnection.java:376) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:265) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:311) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:105) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.io.ChannelEndPoint$1.run(ChannelEndPoint.java:104) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.runTask(EatWhatYouKill.java:338) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.doProduce(EatWhatYouKill.java:315) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.tryProduce(EatWhatYouKill.java:173) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.util.thread.strategy.EatWhatYouKill.run(EatWhatYouKill.java:131) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.util.thread.ReservedThreadExecutor$ReservedThread.run(ReservedThreadExecutor.java:386) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:883) [bundleFile:9.4.43.v20210629]
at org.eclipse.jetty.util.thread.QueuedThreadPool$Runner.run(QueuedThreadPool.java:1034) [bundleFile:9.4.43.v20210629]
at java.lang.Thread.run(Thread.java:829) [?:?]