with t (id, param) as (
 select 1, 'param1' from dual union all
 select 1, 'param99' from dual union all
 select 1, null from dual union all
 select 2, 'param3' from dual union all
 select 2, 'param3' from dual union all
 select 2, 'param4' from dual union all
 select 3, '' from dual union all
 select 3, '' from dual union all
 select 4, null from dual
),
x as (
      select t.*,
             case
               when max(param) over(partition by id) is null then row_number() over(partition by id order by 1)
               when param is null then 0
               else 1
             end flag 
        from  t
     )
select  id,
        param
  from  x
  where flag = 1
  order by id
/

        ID PARAM
---------- -------
         1 param1
         1 param99
         2 param3
         2 param3
         2 param4
         3
         4

7 rows selected.

SQL>