Dbforge alter add column always create NOT NULL field

Hi!

The query of ALTER TABLE ADD COLUMN is automatically concatened by NOT NULL in CodeIgniter working with PostgreSQL

PHP Code:

$this->dbforge = new CI_DB_postgre_forge;
$sql = $this->dbforge->_alter_table('ADD',
                    'data.circuits',
                    'location',
                    'integer');
$this->db->query($sql); 


So I always got an error message when there is already data inside the table: i'm using a french computer

ERREUR: la colonne « location » contient des valeurs NULL
ALTER TABLE "data"."circuits" ADD "location" integer NOT NULL

How to avoid this ?