Changed ponSerialNumber to auth in action.

src/FTTHBundle/Entity/ONU.php

@@ -355,7 +355,11 @@ class ONU implements DeviceInterface, TenancyIdTraitInterface, LocationInterface
      */
     public function setMac($mac)
     {
-        $this->mac = strtolower($mac);
+        if(!empty($mac)) {
+            $this->mac = strtolower($mac);
+        } else {
+            $this->mac = null;
+        }
 
         return $this;
     }