How to disable the In Array validator in Zend Form?

When we use multiple select or checkbox option, there is default validator so that the value should not be empty. We can bypass it using the function setRegisterInArrayValidator
 
   Ex: $selCategories = new Zend_Form_Element_MultiCheckbox('categories', array(
                        'multiOptions' => $categories));
         $selCategories->setRegisterInArrayValidator(false);