// Symfony\Bridge\Doctrine\Form\ChoiceList\ORMQueryBuilderLoader.php
    public function getEntitiesByIds($identifier, array $values)
    {
         //...
         if (in_array($metadata->getTypeOfField($identifier), array('integer', 'bigint', 'smallint'))) {
            $parameterType = Connection::PARAM_INT_ARRAY;

            // Filter out non-integer values (e.g. ""). If we don't, some
            // databases such as PostgreSQL fail.
            $values = array_values(array_filter($values, function ($v) {
                return (string) $v === (string) (int) $v;
            }));
         } 
         //...
    }
}