private bool CompareDocumentWrappedField(FieldAsDocumentExpression a, FieldAsDocumentExpression b)
 {
     return(a.FieldName == b.FieldName &&
            Compare(a.Expression, b.Expression));
 }
 protected internal virtual Expression VisitDocumentWrappedField(FieldAsDocumentExpression node)
 {
     return(node.Update(
                Visit(node.Expression)));
 }