I'm getting NotSupportedException ($project or $group does not support {document}) on very simple join statement:

from s in collection1
join r in collection2 on s.ForeignKey equals r.Id
select s

But everything works great when objects from another collection are projected.

from s in collection1
join r in collection2 on s.ForeignKey equals r.Id
select r

It seems that query translator can't parse document expression.