Fixed QuerySet.raw_aggregate() when some documents don't contain all model fields

[Jibola]

If there exists a document that fits the query criteria but does not have most of the expected keys, it will force every subsequent document to also not render those values.

class Table(models.Model): brand = models.CharField(...) volume = models.IntegerField(...) # intentionally left out unit

Documents:

{ _id: 1, "brand": "SPAM" }, { _id: 2, "brand": "SPAM", "volume": 16, "unit": "oz", ... } 

In the above example, Table.objects.raw_aggregate([]) would yield...

SPAM_OBJECT_1.brand == "SPAM" SPAM_OBJECT_2.brand == "SPAM" SPAM_OBJECT_2.volume == 16 <-- Additional DB query SPAM_OBJECT_2.unit (AttributeError)