Adding zero-value records in a query using cumulative analytical functions

Input and code:

with data as (
  select 1 id, 'A' name, 'fruit' r_group, '2007' year, '04' month, 5 sales from dual union all
  select 2 id, 'Z' name, 'fruit' r_group, '2007' year, '04' month, 99 sales from dual union all
  select 3 id, 'A' name, 'fruit' r_group, '2008' year, '05' month, 10 sales from dual union all
  select 4 id, 'B' name, 'vegetable' r_group, '2008' year,  '07'  month, 20 sales from dual
)

select year,
       month,
       r_group,
       sum(sales) sales,
       sum(opening) opening,
       sum(closing) closing
from (
  select t.*,
         (sum(sales) over (partition by name, r_group
                           order by year, month
                           rows between unbounded preceding and current row
                          ) -sales ) as opening,
         sum(sales) over (partition by name, r_group
                          order by year, month
                          rows between unbounded preceding and current row
                         ) as closing
  from data t
)
group by year, month, r_group
order by year, month

Output:

year   |   month   |  r_group   | sales   |  opening  |  closing    |
2007   |     04    |    fruit   |  104    |    0      |    104      |
2008   |     05    |    fruit   |  10     |    5      |    15       |
2008   |     07    | vegetable  |  20     |    0      |    20       | 

I want the output to be like the following:

year   |   month   |  r_group   | sales   |  opening  |  closing    |
2007   |     04    |    fruit   |  104    |    0      |    104      |
2008   |     05    |    fruit   |  10     |    104    |    114      |
2008   |     07    | vegetable  |  20     |    0      |    20       | 

I can achieve the desired output only by adding a zero-valued record in the data for month=05 and for name = 'Z' like this:

select 1 id, 'A' name, 'fruit' r_group, '2007', year '04' month, 5 sales from dual union all
select 2 id, 'Z' name, 'fruit' r_group, '2007', year '04' month, 99 sales from dual union all
select 3 id, 'A' name, 'fruit' r_group, '2008', year '05' month, 10 sales from dual union all
select 4 id, 'Z' name, 'fruit' r_group, '2008', year '05' month, 0 sales from dual union all
select 5 id, 'B' name, 'vegetable' r_group, '2008', year '07' month, 20 sales from dual ))

However, I want to know if I can do this as part of the select query without having to edit the data itself.