Appel de la Procédure Stockée avec Null Paramètre de Données dans SQL Server

EXECUTE listCustomer null, Null, Null, Null, Null, Null, Null, Null, 
    Null, Null, 'customer_id', 'asc' 

Je veux sélectionner tous les clients s'il n'est pas défini tout filteration. Ci-dessous la procédure stockée:

ALTER PROCEDURE [dbo].[listCustomer] 
-- Add the parameters for the stored procedure here
@customer_id int = 0
, @customer_name varchar(111) = null
, @customer_email varchar(111) = null
, @customer_phone varchar(22) = null
, @customer_fax varchar(22) = null
, @customer_address varchar(255) = null
, @customer_contact_person varchar(50) = null
, @gl_account_id int = 0
, @createdon datetime = null
, @modifiedon datetime = null
, @order_by varchar(50) = 'customer_id'
, @sort_order varchar (5) = 'asc'
AS
BEGIN
-- SET NOCOUNT ON added to prevent extra result sets from
-- interfering with SELECT statements.
SET NOCOUNT ON;
-- Insert statements for procedure here
select
c.*
, ga.gl_account_title
from
customer c
left join   gl_account ga
on
c.gl_account_id = ga.gl_account
where
c.customer_id = ISNULL(@customer_id,c.customer_id)
and
c.customer_name like '%'+isnull(@customer_name,c.customer_name)+'%'
and
c.customer_email = ISNULL(@customer_email,c.customer_email) 
and
c.customer_phone = ISNULL(@customer_phone,c.customer_phone)
and
c.customer_fax = ISNULL(@customer_fax,c.customer_fax)
and
c.customer_address like '%'+ISNULL(@customer_address,c.customer_address)+'%'
and
c.customer_contact_person = ISNULL(@customer_contact_person,c.customer_contact_person)
and
c.gl_account_id = ISNULL(@gl_account_id,c.gl_account_id)
and
c.createdon = ISNULL(@createdon,c.createdon)
--and
--c.modifiedon = ISNULL(@modifiedon,c.modifiedon)
order by 
case when @sort_order = 'asc' then
case
when @order_by = 'customer_id' then cast(c.customer_id as varchar)
when @order_by = 'customer_name' then c.customer_name
when @order_by = 'customer_contact_person' then c.customer_contact_person
when @order_by = 'gl_acount_id' then cast(c.gl_account_id as varchar)
when @order_by = 'createdon' then cast(c.createdon as varchar)
when @order_by = 'modifiedon' then cast(c.modifiedon as varchar)
end
end asc
, case when @sort_order = 'desc' then
case
when @order_by = 'customer_id' then cast(c.customer_id as varchar)
when @order_by = 'customer_name' then c.customer_name
when @order_by = 'customer_contact_person' then c.customer_contact_person
when @order_by = 'gl_acount_id' then cast(c.gl_account_id as varchar)
when @order_by = 'createdon' then cast(c.createdon as varchar)
when @order_by = 'modifiedon' then cast(c.modifiedon as varchar)
end
end desc
END

quand je décommentez modifiedon à la condition de "où" déclaration qu'il me donne pas de réponse moyen 0 lignes. D'autre quand je suis en commentaire donc c'est de me donner la réponse correcte.

Je pense que ça se passe, car il n'y a rien rempli dans la colonne modifié et il est mis à NULL.

S'il vous plaît dites-moi où je me trompe dans ce.

Désolé pour l'anglais!