return null when where has no result

hi,
i have a serious problem with a query i wrote.
i structured something like this:

select employee, sum(turnover), sum(profit_margin)
from -table-
where month='april' and status='closed'
group by employee

the problem is when theres an employee not having any turnover and/or profit margin in a project with status other than closed in a specific month his name is not in the result.

but i want his name to be in the list with sum of turnover = null an profit margin = null.

thank u in advance.
if u have any trouble comprehending the problem, please write too, i'll try to explain it better.