Remove NULL (Blank) Items from DropDownList in ASP.Net

hi

I have house_info table in database and I have dropdownlist in my page that bind it from Shoppingcenter columns from house_info table...

in Shoppingcenter column in some rows are data and  some rows are NULL

now when I bind dropdown list it shows space in first Item after that it shows other Item that bind from house_info table I mean in dropdownlist shows NULL value (Space) that is in Shoppingcenter column

below is SP

ALTER procedure [dbo].[selectcentercityS] 
@city nvarchar(30)
,@region nvarchar(5)
,@district nvarchar(30)
as
begin
select distinct Shoppingcenter
from House_Info
where (city=@city or @city='همه')and(Region=@region or @region='همه')and (district=@district or @district='همه') and (H_name!=N'املاک') and (H_name1=N'وسایل منزل و اداری')
order by Shoppingcenter asc
end

I don't want it shows space in dropdownlist

what should I do?

Best Regards

Neda