Fix for possible NPE that could happen due to null device or null property list.

components/mobile-plugins/mobile-base-plugin/org.wso2.carbon.device.mgt.mobile/src/main/java/org/wso2/carbon/device/mgt/mobile/util/MobileDeviceManagementUtil.java

@@ -73,10 +73,12 @@ public class MobileDeviceManagementUtil {
 	}
 
 	private static String getPropertyValue(Device device, String property) {
+        if (device != null && device.getProperties() != null) {
             for (Device.Property prop : device.getProperties()) {
                 if (property.equals(prop.getName())) {
                     return prop.getValue();
                 }
+            }
         }
 		return null;
 	}