Denon AH-3500 receiver reported offline, errors in log file

I have Denon AH-3500 and I think it was working fine with 3.1.0.M2.
On 3.1.0M3 the device is offline. If I delete the thing representing the receiver and then scan again the received is detected but shown as offline. Telnet is enabled and I think it should be as the device supports HEOS.
Log file has the following error message

2021-04-25 10:34:39.247 [ERROR] [ore.common.registry.AbstractRegistry] - Cannot inform the listener “org.openhab.core.thing.internal.ChannelLinkNotifier@210e301d” about the “ADDED” event: null
java.lang.NullPointerException: null
at org.openhab.binding.denonmarantz.internal.connector.telnet.DenonMarantzTelnetConnector.internalSendCommand(DenonMarantzTelnetConnector.java:270) ~[?:?]
at org.openhab.binding.denonmarantz.internal.connector.DenonMarantzConnector.sendInputCommand(DenonMarantzConnector.java:82) ~[?:?]
at org.openhab.binding.denonmarantz.internal.handler.DenonMarantzHandler.handleCommand(DenonMarantzHandler.java:118) ~[?:?]
at org.openhab.core.thing.binding.BaseThingHandler.channelLinked(BaseThingHandler.java:177) ~[?:?]
at org.openhab.binding.denonmarantz.internal.handler.DenonMarantzHandler.channelLinked(DenonMarantzHandler.java:422) ~[?:?]
at org.openhab.core.thing.internal.ChannelLinkNotifier.lambda$3(ChannelLinkNotifier.java:72) ~[?:?]
at org.openhab.core.thing.internal.ChannelLinkNotifier.call(ChannelLinkNotifier.java:96) ~[?:?]
at org.openhab.core.thing.internal.ChannelLinkNotifier.added(ChannelLinkNotifier.java:72) ~[?:?]
at org.openhab.core.thing.internal.ChannelLinkNotifier.added(ChannelLinkNotifier.java:1) ~[?:?]
at org.openhab.core.common.registry.AbstractRegistry.notifyListeners(AbstractRegistry.java:367) [bundleFile:?]
at org.openhab.core.common.registry.AbstractRegistry.notifyListenersAboutAddedElement(AbstractRegistry.java:400) [bundleFile:?]
at org.openhab.core.thing.link.ItemChannelLinkRegistry.notifyListenersAboutAddedElement(ItemChannelLinkRegistry.java:138) [bundleFile:?]
at org.openhab.core.thing.link.ItemChannelLinkRegistry.notifyListenersAboutAddedElement(ItemChannelLinkRegistry.java:1) [bundleFile:?]
at org.openhab.core.common.registry.AbstractRegistry.added(AbstractRegistry.java:175) [bundleFile:?]
at org.openhab.core.common.registry.AbstractRegistry.added(AbstractRegistry.java:1) [bundleFile:?]
at org.openhab.core.common.registry.AbstractProvider.notifyListeners(AbstractProvider.java:60) [bundleFile:?]
at org.openhab.core.common.registry.AbstractProvider.notifyListeners(AbstractProvider.java:79) [bundleFile:?]
at org.openhab.core.common.registry.AbstractProvider.notifyListenersAboutAddedElement(AbstractProvider.java:83) [bundleFile:?]
at org.openhab.core.model.thing.internal.GenericItemChannelLinkProvider.createItemChannelLink(GenericItemChannelLinkProvider.java:106) [bundleFile:?]
at org.openhab.core.model.thing.internal.GenericItemChannelLinkProvider.processBindingConfiguration(GenericItemChannelLinkProvider.java:76) [bundleFile:?]
at org.openhab.core.model.item.internal.GenericItemProvider.internalDispatchBindings(GenericItemProvider.java:372) [bundleFile:?]
at org.openhab.core.model.item.internal.GenericItemProvider.internalDispatchBindings(GenericItemProvider.java:341) [bundleFile:?]
at org.openhab.core.model.item.internal.GenericItemProvider.processBindingConfigsFromModel(GenericItemProvider.java:212) [bundleFile:?]
at org.openhab.core.model.item.internal.GenericItemProvider.modelChanged(GenericItemProvider.java:407) [bundleFile:?]
at org.openhab.core.model.core.internal.ModelRepositoryImpl.notifyListeners(ModelRepositoryImpl.java:301) [bundleFile:?]
at org.openhab.core.model.core.internal.ModelRepositoryImpl.addOrRefreshModel(ModelRepositoryImpl.java:139) [bundleFile:?]
at org.openhab.core.model.core.internal.folder.FolderObserver.checkFile(FolderObserver.java:249) [bundleFile:?]
at org.openhab.core.model.core.internal.folder.FolderObserver.processWatchEvent(FolderObserver.java:312) [bundleFile:?]
at org.openhab.core.service.WatchQueueReader.lambda$3(WatchQueueReader.java:322) [bundleFile:?]
at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515) [?:?]
at java.util.concurrent.FutureTask.run(FutureTask.java:264) [?:?]
at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304) [?:?]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
at java.lang.Thread.run(Thread.java:834) [?:?]