Linq to Object / XML where元素不存在

var doc3 = XDocument.Load(@"C:\Projects\ScanBandConfigTesting\ScanBandConfigTesting\ScanBandConfigSmall.xml");

var scanBand = new ScanBand()
{
    ListOfForms = (from form in doc3.Descendants("form")
                    select new ScanBandForm()
                    {
                        FormTypes = form.Attribute("types").Value,
                        ScanBandNumber = form.Attribute("number").Value,
                        ListOfRows = (from row in form.Descendants("row")
                                        select new ScanBandRow()
                                        {
                                            AllowSpaces = row.Element("allowSpaces").Value.ToLower() == "true",
                                            SplitCharacter = row.Element("splitCharacter").Value,
                                            ListOfColumns = (from column in row.Descendants("column")
                                                            select new ScanBandColumn()
                                                            {
                                                                AlwaysKey = column.Element("allwaysKey").IsEmpty ? false : column.Element("allwaysKey").Value.ToLower() == "true",
                                                                DataTypeString = column.Element("dataType").IsEmpty ? string.Empty : column.Element("dataType").Value,
                                                                MatchingFieldName = column.Element("matchingFieldName").IsEmpty ? string.Empty : column.Element("matchingFieldName").Value,
                                                                NonField = column.Element("nonField").IsEmpty ? false : column.Element("nonField").Value.ToLower() == "true",
                                                                RegularExpressionString = column.Element("regularExpression").IsEmpty ? string.Empty : column.Element("regularExpression").Value,
                                                            }).ToList()
                                        }).ToList()
                    }).ToList()
};
var doc3 = XDocument.Load(@"C:\Projects\ScanBan