showing null in field values

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SQL-Server

SQL-Server-2008

hi to all

here in this code
modname_vc is my output


this is my output
null
computer
Accounts
HR
..
.
.
.
can you tell me why the first value is null
in sec_modules there is no null

procedure [dbo].[proc_modules_for_user] (@uid nvarchar (50))
as
select  distinct sec_modules.modname_vc
from sec_umrf_details 
left join sec_mrf_details on sec_umrf_details.mrfno_int = sec_mrf_details.mrfno_int 			
left join sec_modules on sec_modules.modid_int = sec_mrf_details.modid_int
where	
sec_umrf_details.deleted_int=0 and sec_umrf_details.userid_vc=@uid