protected internal virtual Expression VisitGroupingKey(GroupingKeyExpression node)
 {
     return node.Update(Visit(node.Expression));
 }
 protected internal virtual Expression VisitGroupingKey(GroupingKeyExpression node)
 {
     return(node.Update(Visit(node.Expression)));
 }
 private BsonValue TranslateGroupingKey(GroupingKeyExpression node)
 {
     return TranslateValue(node.Expression);
 }