Go driver, run aggregation pipeline with $merge

hi,

I am new to mongo and was looking for ways to trigger the on-demand-materialised view in Go driver.

I tried running the aggregation pipeline in Go with $merge. But seems like it’s not performing anything.

collection := client.Database("poc").Collection("po_new_audit")

	matchStg := bson.D{{"$match", bson.D{{"synced", false}}}}
	addFieldStg1 := bson.D{{"$addFields", bson.D{{"audit_type", "purchase_order"}}}}
	lookupStg := bson.D{{"$lookup", bson.D{{"from", "user"}, {"localField", "who.id"}, {"foreignField", "_id"}, {"as", "user_details"}}}}
	unwindStg1 := bson.D{{"$unwind", "$user_details"}}
	addFieldStg2 := bson.D{{"$addFields", bson.D{{"breadcrumbs", bson.D{{"po_id", "$entity_id"}}}}}}
	projectStg := bson.D{{"$project", bson.D{{"_id", "1"}, {"what", "1"}, {"when", "1"}, {"user_details", "1"}, {"breadcrumbs", "1"}, {"audit_type", "1"}}}}
	mergeStg := bson.D{{"$merge", bson.D{{"into", "audit"}}}}
	c, err := collection.Aggregate(context.TODO(), mongo.Pipeline{matchStg, addFieldStg1, lookupStg, unwindStg1, addFieldStg2, projectStg, mergeStg})
	if err != nil {
		panic(err)
	}

	var loaded []bson.M
	if err = c.All(context.TODO(), &loaded); err != nil {
		panic(err)
	}
	fmt.Println(loaded)

The aggregation works till the projectStg and cursor gives the return values. But adding $merge doesn’t give an error but returns empty cursor. Also, the merge document doesn’t get updated.

Any pointers will really help.

Regards,
Sayan