This istruction is not supported in VB
Dim postQuerable As IQueryable(Of Post) = New MongoDB.Driver.Linq.MongoQueryable(Of Post)(New MongoQueryProvider(posts))
Dim postsWithComments = From p In postQuerable
Where p.Lista Is Nothing And p.Lista.Count > 0
Select p

but this is
var postsWithComments = from p in posts.AsQueryable()
where p.Comments != null && p.Comments.Count > 0
select p;

Do you think to implement a full support for VB ?