RecursionBsonDocumentRemoveNulls.cs

using MongoDB.Bson;

public static class BsonDocumentExtentions
{
    public static void RemoveNullElements(this BsonDocument documents)
    {
        RemoveNulls(documents);
    }
    public static BsonDocument RemoveNulls(BsonDocument document)
    {
        var counter = document.ElementCount - 1;
        var elem = document.ElementAt(counter);
        while(counter >= 0){
            RemoveIfNull(elem, document);
            counter--;
            if(counter < 0) break;
            elem = document.ElementAt(counter);
        }
        return document;
    }
    public static void RemoveIfNull(BsonElement element, BsonDocument document)
    {
        if(element.Value == BsonNull.Value || element.Value == null){
            document.RemoveElement(element);
        } else {
            try{
                RemoveNulls(element.Value.ToBsonDocument());
                if(element.Value.ToBsonDocument().ElementCount == 0){
                    document.RemoveElement(element);
                }
            }catch(InvalidOperationException e){
                Console.WriteLine($"Exception happened trying to remove nulls = {e}");
            }
        }
    }
}