Invalid condition generation in filtered positional operator

[nmarcin92]

Using the exact example from docs:
https://www.mongodb.com/docs/manual/reference/operator/update/positional-filtered/#update-all-array-elements-that-match-arrayfilters

case class Grades(id: Grades.ID, grades: List[Grade]) extends MongoEntity[Int]
object Grades extends MongoEntityCompanion[Grades]

case class Grade(grade: Int, mean: Int, std: Int)
object Grade extends MongoDataCompanion[Grade]

val update = Grades.ref(_.grades).updateFiltered(
 filter = _.ref(_.grade).gte(85),
 update = _.ref(_.mean).set(100)
)

We can see that the generated array query looks as follow:

println(update.toBsonAndArrayFilters._2.asScala.head.toJson)
> {"filter0": {"grade": {"$gte": 85}}}

instead of {"filter0.grade" : {"$gte": 85}}}

This actually matches on documents in the array that are equal to {"grade": {"$gte": 85}}, instead of evaluating the condition on its fields, so it makes it impossible to actually query the documents in array.