[tradfri] fix null pointer exception when sending command to a device that is offline

[robnielsen]

This fixes the following error when a Tradfri device is offline:

2022-02-22 09:43:07.970 [DEBUG] [internal.handler.TradfriThingHandler] - Sending payload: {"3312":[{"5850":0}],"3":null}
2022-02-22 09:43:07.981 [ERROR] [nal.common.AbstractInvocationHandler] - An error occurred while calling method 'ThingHandler.handleCommand()' on 'org.openhab.binding.tradfri.internal.handler.TradfriPlugHandler@e7b2d8': null
java.lang.NullPointerException: null
        at org.openhab.binding.tradfri.internal.handler.TradfriThingHandler.set(TradfriThingHandler.java:139) ~[?:?]
        at org.openhab.binding.tradfri.internal.handler.TradfriPlugHandler.setState(TradfriPlugHandler.java:58) ~[?:?]
        at org.openhab.binding.tradfri.internal.handler.TradfriPlugHandler.handleCommand(TradfriPlugHandler.java:73) ~[?:?]
        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.openhab.core.internal.common.AbstractInvocationHandler.invokeDirect(AbstractInvocationHandler.java:154) [bundleFile:?]
        at org.openhab.core.internal.common.InvocationHandlerSync.invoke(InvocationHandlerSync.java:59) [bundleFile:?]
        at com.sun.proxy.$Proxy489.handleCommand(Unknown Source) [?:?]
        at org.openhab.core.thing.internal.profiles.ProfileCallbackImpl.handleCommand(ProfileCallbackImpl.java:80) [bundleFile:?]
        at org.openhab.core.thing.internal.profiles.SystemDefaultProfile.onCommandFromItem(SystemDefaultProfile.java:48) [bundleFile:?]
        at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
        at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[?:?]
        at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[?:?]
        at java.lang.reflect.Method.invoke(Method.java:566) ~[?:?]
        at org.openhab.core.internal.common.AbstractInvocationHandler.invokeDirect(AbstractInvocationHandler.java:154) [bundleFile:?]
        at org.openhab.core.internal.common.Invocation.call(Invocation.java:52) [bundleFile:?]
        at java.util.concurrent.FutureTask.run(FutureTask.java:264) [?:?]
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) [?:?]
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) [?:?]
        at java.lang.Thread.run(Thread.java:829) [?:?]

It now logs:

2022-02-22 09:58:52.159 [DEBUG] [internal.handler.TradfriThingHandler] - coapClient is null!

[lolodomo]

Please also consider potential NPE in method setStatus and in methods handleCommand in all handlers when handling REFRESH command.

[cweitkamp]

At best we should change the annotation of the property coapClient from @NinNullByDefault({}) to @Nullable to find all possible places for an NPE.

[lolodomo]

At best we should change the annotation of the property coapClient from @NinNullByDefault({}) to @Nullable to find all possible places for an NPE.

I fully agree.

[robnielsen]

At best we should change the annotation of the property coapClient from @NinNullByDefault({}) to @nullable to find all possible places for an NPE.

done

[lolodomo]

LGTM