code: static BsonDocument sanitizeDocument(final BsonDocument document) {
      if (document == null) {
        return null;
      }
      if (document.containsKey(DOCUMENT_VERSION_FIELD)) {
        final BsonDocument clonedDoc = document.clone();
        clonedDoc.remove(DOCUMENT_VERSION_FIELD);
  
        return clonedDoc;
      }
      return document;
    }
docs: Given a BSON document, remove any forbidden fields and return the document. If no changes are
  made, the original document reference is returned. If changes are made, a cloned copy of the
  document with the changes will be returned.
  
  @param document the document from which to remove forbidden fields
  
  @return a BsonDocument without any forbidden fields.