fixed issue when default value is set for qos

components/extensions/cdmf-transport-adapters/output/org.wso2.carbon.device.mgt.output.adapter.mqtt/src/main/java/org/wso2/carbon/device/mgt/output/adapter/mqtt/util/MQTTBrokerConnectionConfiguration.java

@@ -116,7 +116,7 @@ public class MQTTBrokerConnectionConfiguration {
             keepAlive = MQTTEventAdapterConstants.ADAPTER_CONF_DEFAULT_KEEP_ALIVE;
         }
         String qosVal = globalProperties.get(MQTTEventAdapterConstants.ADAPTER_MESSAGE_QOS);
-        if (qosVal == null || qosVal.isEmpty()) {
+        if (qosVal != null && !qosVal.isEmpty()) {
             this.qos = Integer.parseInt(qosVal);
         } else {
             qosVal = eventAdapterConfiguration.getStaticProperties().get(MQTTEventAdapterConstants.ADAPTER_MESSAGE_QOS);