Use Condition Parameters in SQL Server Database Query

i have a stored procedure with few params

the sp has query as follows

select * from register where code=@pcode and gender = @pgender and name like @pname+'%'

the user can enter all  the 3 filter parameters or can choose any one

my issue is

if the user passes pname param and other 2 params are passed as dbnull i AM  not getting the records

as my stmt wuld become

select * from register where code='' and gender = '' and name like A+'%'

but the stmt should be 

select * from register where  name like A+'%'