mysql order by, null first, and DESC after

How can I order DESC by a field, but list the NULL values first?

So I'm having a table:

reuestId | offerId | offerTitle
1        | 1       | Alfa
NULL     | 2       | Beta
2        | 3       | Gamma

I want to select them so that the results would be:

NULL | 2 | Beta
2    | 3 | Gamma
1    | 1 | Alfa