PHPRunner inserts a ( '' ) 2 quoted value with nothing be

Hello
I have 2 tables

1. articulo
   with 2 fields of barcodes
   idartic serial NOT NULL
   
   descartic character varying(100) NOT NULL,
   
   codbarra1 character varying(30)
   
   codbarra2 character varying(30)
   and
   
2. codigobarra
   idcodigodebarra serial NOT NULL,
   
   idtipocodigodebarra integer NOT NULL,
   
   idarticulo integer NOT NULL,
   
   codigodebarra character varying(30) NOT NULL,
   And a Trigger Function, on Insert event over table articulo
   CREATE OR REPLACE FUNCTION insert_precioventa_codbarra()
   
   RETURNS "trigger" AS
   
   $BODY$
   BEGIN
   
   IF TG_OP = 'INSERT' THEN
   IF NEW.codbarra1 IS NOT NULL THEN
   
   INSERT INTO codigodebarra (idtipocodigodebarra,idarticulo,codigodebarra)
   
   VALUES (2,NEW.idarticulo,NEW.codbarra1);
   
   END IF;
   IF NEW.codbarra2 IS NOT NULL THEN
   
   INSERT INTO codigodebarra (idtipocodigodebarra,idarticulo,codigodebarra)
   
   VALUES (2,NEW.idarticulo,NEW.codbarra2);
   
   END IF;
   RETURN NEW;
   
   END;
   
   $BODY$
   
   LANGUAGE 'plpgsql' VOLATILE;
   
   ALTER FUNCTION insert_precioventa_codbarra() OWNER TO postgres;
   I have made a Project in PHPRunner and built it
   In the articulo add page when I register a product and leave empty (NULL) the field codbarra1 and codbarra2 the PHPRunner inserts a ( '' ) 2 quoted value with nothing between ? Why??????
   
   It makes my unique constraint to block the Insert because it inserts '' in every register
   Hugo - Paraguay