I’ve got following struct:
(Golang and mongo)

    Account struct {
        ID            primitive.ObjectID `bson:"_id" json:"id,omitempty"`
        AccountId     string
        SessionId     string
        Template      string
        JoinDate      time.Time
        // ...
    }

When I try to find duplicates (and remove them) bofore I create unique index on those fields: AccountId + SessionId + Template + JoinDate.
So this functions is called with AccountId,SessionId,Template,JoinDate as fields

func (ms *MongoStorage) deleteDuplicates(col string, fields ...string) (int64, error) {
    type findDuplicatesResult struct {
        Count     int64                `bson:"count"`
        ObjectIDs []primitive.ObjectID `bson:"objectIDs"`
        Id        map[string]string    `bson:"_id"`
    }

    var (
        dc           int64
        fieldsFilter = make(primitive.M)
        mongoColl    = ms.getCol(col)
    )
    for _, field := range fields {
        fieldsFilter[field] = fmt.Sprintf("$%s", field)
    }
    findDuplicatesFilter := primitive.A{
        primitive.M{"$group": primitive.M{
            "_id":       fieldsFilter,
            "objectIDs": primitive.M{"$push": "$_id"},
            "count":     primitive.M{"$sum": 1},
        }},
        primitive.M{"$match": primitive.M{"count": primitive.M{"$gt": 1}}},
    }
    results := []findDuplicatesResult{}
    var cur *mongo.Cursor
    cur, err := mongoColl.Aggregate(ms.GetContext(), findDuplicatesFilter)
    if err != nil {
        return 0, err
    }
    err = cur.All(ms.GetContext(), &results)
    if err != nil {
        return 0, err
    }

if len(results) > 0 {
        for _, result := range results {
            deleteFilter := primitive.M{
                "_id": primitive.M{
                    "$in": result.ObjectIDs[1:],
                },
            }
            mdr, err := mongoColl.DeleteMany(ms.GetContext(), deleteFilter)

This:

err = cur.All(ms.GetContext(), &results)
    if err != nil {
        return 0, err
    }

causes following error:

"cannot decode UTC datetime into a string type"

https://www.mongodb.com/community/forums/t/best-way-to-remove-duplicates-for-millions-of-records/178245
because JoinDate is type of time.Time
Are there any ways to fix this?