T-sql 2012 accept null parameter values

Question

The following t-sql 2012 works fine in sql management studio. However when I place it in a .net 2010 web form application, I am told the sql does not work when the parameter values are null. Thus can you tell me what I can change in the sql below that will
accept null as 3 possible input values?
SELECT i.[lastName]
            ,i.[firstName] 
            ,i.[middleName]
            ,i.[suffix] 
            ,a.[userid]
            ,a.schoolnum 
            ,a.spa 
            ,a.mrref
            from [OPS].[dbo].[Identity] i 
            inner join  [OPS].[dbo].[Person] p on i.identityID = p.currentIdentityID 
            inner join [OPS].[dbo].[UserAccount] u on u.personID = p.personID 
            inner join [CampusOps].[dbo].[AtnLtrUsers] a on a.userid =u.username
                   where (i.[lastName] like  '%' + @lname  + '%' or i.[firstName] like'%' +
@fname + '%'
                   or i.[middleName]  like'%' + @mname + '%')
or (@fname is null and @lname is null and @mname is null)
        order by  i.[lastName], i.[firstName], i.[middleName]"

Answer 1

You should create a stored procedure for this.
create procedure GetNames
(@lname varchar(max) = null, @fname varchar(max) = null, @mname varchar(max) = null)
as
begin
SELECT i.[lastName]
,i.[firstName]
,i.[middleName]
,i.[suffix]
,a.[userid]
,a.schoolnum
,a.spa
,a.mrref
from [OPS].[dbo].[Identity] i
inner join [OPS].[dbo].[Person] p on i.identityID = p.currentIdentityID
inner join [OPS].[dbo].[UserAccount] u on u.personID = p.personID
inner join [CampusOps].[dbo].[AtnLtrUsers] a on a.userid =u.username
where (i.[lastName] like '%' + @lname + '%' or @lname is null) and
(i.[firstName] like'%' + @fname + '%' or @fname is null) and
(i.[middleName] like'%' + @mname + '%' or @mname is null)
order by i.[lastName], i.[firstName], i.[middleName]
end
Also keep in mind that NULL is different than an empty string but it should work exactly like a null anyway (unless your columns/fields are also NULLable).