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java.lang.NullPointerException: 	at org.eclipse.paho.client.mqttv3.MqttTopic.validate(MqttTopic.java:147)	at org.eclipse.paho.client.mqttv3.MqttAsyncClient.unsubscribe(MqttAsyncClient.java:917)	at org.eclipse.paho.client.mqttv3.MqttAsyncClient.unsubscribe(MqttAsyncClient.java:898)	at com.ibm.iotf.devicemgmt.device.ManagedDevice.unsubscribe(ManagedDevice.java:636)	at com.ibm.iotf.devicemgmt.device.ManagedDevice$ManagedDeviceClient.unsubscribe(ManagedDevice.java:977)	at com.ibm.internal.iotf.devicemgmt.handler.DMRequestHandler.clearRequestHandlers(DMRequestHandler.java:239)	at com.ibm.iotf.devicemgmt.device.ManagedDevice.sendUnmanageRequest(ManagedDevice.java:530)	at com.ibm.iotcloud.test.jmeter.sampler.dm.FirmwareActions.deleteDevice(FirmwareActions.java:193)	at com.ibm.iotcloud.test.jmeter.sampler.dm.FirmwareActions.teardownTest(FirmwareActions.java:256)	at org.apache.jmeter.protocol.java.sampler.JavaSampler.testEnded(JavaSampler.java:292)	at org.apache.jmeter.engine.StandardJMeterEngine.notifyTestListenersOfEnd(StandardJMeterEngine.java:215)	at org.apache.jmeter.engine.StandardJMeterEngine.run(StandardJMeterEngine.java:436)	at java.lang.Thread.run(Unknown Source)