Crear Clase que herede de ObjectModel

[Tito Samuel]

Hola, estoy intentando crear una clase que hereda de ObjectModel, pero al hacer un New, no se carga la pagina lo cual indica que hay un error, les indico, e instanciado la clase de las siguientes formas:

$cupo = new Cupo();
$cupo = new Cupo($id);

Pero ninguna funciona, aqui les dejo el codigo de la clase:

class        Cupo extends ObjectModel
{    
   /** @var integer Currency id */
   public         $id_currency;

   /** @var string Secure key */
   public        $secure_key;

   /** @var string Payment method id */
   public         $payment;

   /** @var string Payment module */
   public         $module;

   /** @var float Total del cupo */
   public         $total_cupo;

   /** @var float Total a comprar */
   public         $total_compra;

   /** @var string Invoice creation date */
   public         $invoice_date;

   /** @var string Delivery creation date */
   public         $delivery_date;

   /** @var boolean Order validity (paid and not canceled) */
   public         $valid;

   /** @var string Object last modification date */
   public         $date_upd;

   protected $tables = array ('cupo');

   protected    $fieldsRequired = array('id_currency', 'payment', 'total_compra');
   protected    $fieldsSize = array('payment' => 32);
   protected    $fieldsValidate = array(        
       'id_currency' => 'isUnsignedId',
       'secure_key' => 'isMd5',
       'payment' => 'isGenericName',        
       'total_cupo' => 'isPrice',
       'total_compra' => 'isPrice'
       );

   /* MySQL does not allow 'order' for a table name */
   protected     $table = 'cupo';
   protected     $identifier = 'id_customer';

   public function getFields()
   {
       parent::validateFields();

       $fields['secure_key'] = pSQL($this->secure_key);
       $fields['payment'] = pSQL($this->payment);
       $fields['module'] = pSQL($this->module);
       $fields['total_cupo'] = floatval($this->total_cupo);
       $fields['total_compra'] = floatval($this->total_compra);        
       $fields['invoice_date'] = pSQL($this->invoice_date);        
       $fields['valid'] = intval($this->valid) ? 1 : 0;
       $fields['date_upd'] = pSQL($this->date_upd);

       return $fields;
   }    

   public function isLogable()
   {
       return $this->valid;
   }    

   /**
    * Get customer cupo total
    *     
    * @return array Customer cupo
    */
   static public function getCustomerCupo()
   {
       $result = Db::getInstance()->getRow('
       SELECT monto as cp
       FROM `'._DB_PREFIX_.'cupo`
       WHERE `id_customer` = '.intval($this->id));

       return isset($result['cp']) ? $result['cp'] : 0;
   }

   /**
    * Add nuevo registro para cupo por primera vez
    *
    * @param double $monto valor a regarcar en cupo
    * @return boolean Query sucess or not
    */
   public function    addFirstCupo($monto)
   {
       return Db::getInstance()->AutoExecute(_DB_PREFIX_.'cupot', array('id_cupo' => intval($this->id), 'monto' => doubleval($monto), 'date_add' => pSql(date('Y-m-d H:i:s')), 'INSERT');
   }

}

Gracias de antemano por su ayuda

[Tito Samuel]

Ya lo resolvi, era un error en la function addFirstCupo, me faltaba un parentesis.