MS SQL server: Optional Search Parameters

create proc myproc (
 val_1 int,    -- required
 val_2 varchar(32), -- optional
 val_3 int    -- optional
) as

select *
from mytable
where
 col_1 = val_1
 and col_2 like case
  when val_2 = '' then col_2
  else '%' + val_2 + '%'
  end
 and col_3 = case
  when val_3 = 0 then col_3
  else val_3
  end
go