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

@@ -73,11 +73,13 @@ public class MobileDeviceManagementUtil {
 	}
 
 	private static String getPropertyValue(Device device, String property) {
-		for (Device.Property prop : device.getProperties()) {
-			if (property.equals(prop.getName())) {
-				return prop.getValue();
-			}
-		}
+        if (device != null && device.getProperties() != null) {
+            for (Device.Property prop : device.getProperties()) {
+                if (property.equals(prop.getName())) {
+                    return prop.getValue();
+                }
+            }
+        }
 		return null;
 	}