How to make deserialization return null if empty

Question

I'm working in deserialization and right now I'm able to successfully deserialize XML as intended.

However, when I try to deserialize an XML-tag that dosen't exist, I get the NullException error and that is understandable.

I want it to just return null if the tag doesnt exist instead of getting error message but I'm not sure how to do that.

List<FolkbokforingspostTYPE> deserializedList = new List<FolkbokforingspostTYPE>();
deserializedList = Deserialize<List<FolkbokforingspostTYPE>>();

var PostNr = deserializedList.Select(item => item.Personpost.Adresser.Folkbokforingsadress.PostNr).ToList();

In this case, the tag Folkbokforingsadress doesn't always exist.

Instead of getting the error, I just want it to return NULL and move on, how can I do that?

UPDATE:

My deserialization classes:

[XmlRoot(ElementName = "Sekretessmarkering")]
public class Sekretessmarkering
{
    [XmlAttribute(AttributeName = "nil", Namespace = "http://www.w3.org/2001/XMLSchema-instance")]
    public string Nil { get; set; }
}

[XmlRoot(ElementName = "PersonId")]
public class PersonId
{
    [XmlElement(ElementName = "PersonNr")]
    public string PersonNr { get; set; }
}

[XmlRoot(ElementName = "HanvisningsPersonNr")]
public class HanvisningsPersonNr
{
    [XmlAttribute(AttributeName = "nil", Namespace = "http://www.w3.org/2001/XMLSchema-instance")]
    public string Nil { get; set; }
}

[XmlRoot(ElementName = "Mellannamn")]
public class Mellannamn
{
    [XmlAttribute(AttributeName = "nil", Namespace = "http://www.w3.org/2001/XMLSchema-instance")]
    public string Nil { get; set; }
}

[XmlRoot(ElementName = "Aviseringsnamn")]
public class Aviseringsnamn
{
    [XmlAttribute(AttributeName = "nil", Namespace = "http://www.w3.org/2001/XMLSchema-instance")]
    public string Nil { get; set; }
}

[XmlRoot(ElementName = "Namn")]
public class Namn
{
    [XmlElement(ElementName = "Tilltalsnamnsmarkering")]
    public string Tilltalsnamnsmarkering { get; set; }
    [XmlElement(ElementName = "Fornamn")]
    public string Fornamn { get; set; }
    [XmlElement(ElementName = "Mellannamn")]
    public Mellannamn Mellannamn { get; set; }
    [XmlElement(ElementName = "Efternamn")]
    public string Efternamn { get; set; }
    [XmlElement(ElementName = "Aviseringsnamn")]
    public Aviseringsnamn Aviseringsnamn { get; set; }
}

[XmlRoot(ElementName = "ForsamlingKod")]
public class ForsamlingKod
{
    [XmlAttribute(AttributeName = "nil", Namespace = "http://www.w3.org/2001/XMLSchema-instance")]
    public string Nil { get; set; }
}

[XmlRoot(ElementName = "Folkbokforing")]
public class Folkbokforing
{
    [XmlElement(ElementName = "Folkbokforingsdatum")]
    public string Folkbokforingsdatum { get; set; }
    [XmlElement(ElementName = "LanKod")]
    public string LanKod { get; set; }
    [XmlElement(ElementName = "KommunKod")]
    public string KommunKod { get; set; }
    [XmlElement(ElementName = "ForsamlingKod")]
    public ForsamlingKod ForsamlingKod { get; set; }
    [XmlElement(ElementName = "Fastighetsbeteckning")]
    public string Fastighetsbeteckning { get; set; }
    [XmlElement(ElementName = "FiktivtNr")]
    public string FiktivtNr { get; set; }
}

[XmlRoot(ElementName = "CareOf")]
public class CareOf
{
    [XmlAttribute(AttributeName = "nil", Namespace = "http://www.w3.org/2001/XMLSchema-instance")]
    public string Nil { get; set; }
}

[XmlRoot(ElementName = "Utdelningsadress1")]
public class Utdelningsadress1
{
    [XmlAttribute(AttributeName = "nil", Namespace = "http://www.w3.org/2001/XMLSchema-instance")]
    public string Nil { get; set; }
}

[XmlRoot(ElementName = "Folkbokforingsadress")]
public class Folkbokforingsadress
{
    [XmlElement(ElementName = "CareOf")]
    public CareOf CareOf { get; set; }
    [XmlElement(ElementName = "Utdelningsadress1")]
    public Utdelningsadress1 Utdelningsadress1 { get; set; }
    [XmlElement(ElementName = "Utdelningsadress2")]
    public string Utdelningsadress2 { get; set; }
    [XmlElement(ElementName = "PostNr")]
    public string PostNr { get; set; }
    [XmlElement(ElementName = "Postort")]
    public string Postort { get; set; }
}

[XmlRoot(ElementName = "Riksnycklar")]
public class Riksnycklar
{
    [XmlElement(ElementName = "FastighetsId")]
    public string FastighetsId { get; set; }
    [XmlElement(ElementName = "AdressplatsId")]
    public string AdressplatsId { get; set; }
    [XmlElement(ElementName = "LagenhetsId")]
    public string LagenhetsId { get; set; }
}

[XmlRoot(ElementName = "Adresser")]
public class Adresser
{
    [XmlElement(ElementName = "Folkbokforingsadress")]
    public Folkbokforingsadress Folkbokforingsadress { get; set; }
    [XmlElement(ElementName = "Riksnycklar")]
    public Riksnycklar Riksnycklar { get; set; }
}

[XmlRoot(ElementName = "HemortSverige")]
public class HemortSverige
{
    [XmlElement(ElementName = "FodelselanKod")]
    public string FodelselanKod { get; set; }
    [XmlElement(ElementName = "Fodelseforsamling")]
    public string Fodelseforsamling { get; set; }
}

[XmlRoot(ElementName = "Fodelse")]
public class Fodelse
{
    [XmlElement(ElementName = "HemortSverige")]
    public HemortSverige HemortSverige { get; set; }
}

[XmlRoot(ElementName = "Medborgarskap")]
public class Medborgarskap
{
    [XmlElement(ElementName = "MedborgarskapslandKod")]
    public string MedborgarskapslandKod { get; set; }
    [XmlElement(ElementName = "Medborgarskapsdatum")]
    public string Medborgarskapsdatum { get; set; }
}

[XmlRoot(ElementName = "Personpost")]
public class Personpost
{
    [XmlElement(ElementName = "PersonId")]
    public PersonId PersonId { get; set; }
    [XmlElement(ElementName = "HanvisningsPersonNr")]
    public HanvisningsPersonNr HanvisningsPersonNr { get; set; }
    [XmlElement(ElementName = "Namn")]
    public Namn Namn { get; set; }
    [XmlElement(ElementName = "Folkbokforing")]
    public Folkbokforing Folkbokforing { get; set; }
    [XmlElement(ElementName = "Adresser")]
    public Adresser Adresser { get; set; }
    [XmlElement(ElementName = "Fodelse")]
    public Fodelse Fodelse { get; set; }
    [XmlElement(ElementName = "Medborgarskap")]
    public Medborgarskap Medborgarskap { get; set; }
}

[XmlRoot(ElementName = "FolkbokforingspostTYPE")]
public class FolkbokforingspostTYPE
{
    [XmlElement(ElementName = "Sekretessmarkering")]
    public Sekretessmarkering Sekretessmarkering { get; set; }
    [XmlElement(ElementName = "Personpost")]
    public Personpost Personpost { get; set; }
}

UPDATE 2

The entire code:

 class Program
{
        static void Main(string[] args)
        {
            //try
            //{

            List<FolkbokforingspostTYPE> deserializedList = new List<FolkbokforingspostTYPE>();
            deserializedList = Deserialize<List<FolkbokforingspostTYPE>>();

            var PersonalIdentityNumber = deserializedList.Select(item => item.Personpost.PersonId.PersonNr).ToList();
            var FirstName = deserializedList.Select(item => item.Personpost.Namn.Fornamn).ToList();

            var LastName = deserializedList.Select(item => item.Personpost.Namn.Efternamn).ToList();
            var LanKod = deserializedList.Select(item => item.Personpost.Folkbokforing.LanKod).ToList();
            var Kommunkod = deserializedList.Select(item => item.Personpost.Folkbokforing.KommunKod).ToList();

            var UtdelAdress2 = deserializedList.Select(item => item.Personpost.Adresser.Folkbokforingsadress.Utdelningsadress2).ToList();
            var PostNr = deserializedList.Select(item => item?.Personpost?.Adresser?.Folkbokforingsadress?.PostNr).ToList();

            //var PostOrt = deserializedList.Select(item => item.Personpost.Adresser.Folkbokforingsadress.Postort).ToList();

            //var FodelselanKod = deserializedList.Select(item => item.Personpost.Fodelse.HemortSverige.FodelselanKod).ToList();

            //var Fodelseforsamling = deserializedList.Select(item => item.Personpost.Fodelse.HemortSverige.Fodelseforsamling).ToList();

            var MedborgarskapslandKod = deserializedList.Select(item => item.Personpost.Medborgarskap.MedborgarskapslandKod).ToList();

            var Medborgarskapsdatum = deserializedList.Select(item => item.Personpost.Medborgarskap.Medborgarskapsdatum).ToList();


            //var zipped = PersonalIdentityNumber.Zip(FirstName, Tuple.Create);

            //     foreach (var tuple in zipped)
            //     {
            //         //Console.WriteLine(tuple.Item1);
            //         //Console.WriteLine(tuple.Item2);
            //     }

            //Console.WriteLine(PersonalIdentityNumber.Count());

            //for (int i = 0; i < PersonalIdentityNumber.Count; i++)
            //{
            //    var personnummer = PersonalIdentityNumber[i];
            //    var fornamn = FirstName[i];
            //        var efternamn = LastName[i];

            //        var lankod = LanKod[i];
            //        var kommunkod = Kommunkod[i];
            //        var utdelAdress2 = UtdelAdress2[i];
            //        var postNr = PostNr[i];
            //        var postOrt = PostOrt[i];
            //        var fodelselanKod = FodelselanKod[i];
            //        var fodelseforsamling = Fodelseforsamling[i];
            //        var medborgarskapslandKod = MedborgarskapslandKod[i];
            //        var medborgarskapsdatum = Medborgarskapsdatum[i];
            //         use your variables


            //}

            //Console.WriteLine(PersonalIdentityNumber.Count());

            //foreach (var i in PersonalIdentityNumber)
            //{
            //    Console.WriteLine("Personnummer: " + i);

            //    foreach(var a in FirstName)
            //    {
            //        Console.WriteLine("Namn: " + a);
            //    }







            string connetionString = null;


            SqlDataAdapter adpter = new SqlDataAdapter();
            DataSet ds = new DataSet();
            XmlReader xmlFile;



            connetionString = "Data Source=tsrv2062;Initial Catalog=Bums;User ID=BumsUser;Password=2tusen7Bums";


            xmlFile = XmlReader.Create("navetout.xml", new XmlReaderSettings());
            ds.ReadXml(xmlFile);


            using (var connection = new SqlConnection(connetionString))
            {
                connection.Open();



                DateTime datum = DateTime.Now;

                SqlCommand command1 = new SqlCommand("UPDATE Seamen SET FirstName = @FirstName, LastName = @LastName, NationalRegistrationCountyCode = @NationalRegistrationCountyCode, NationalRegistrationMunicipalityCode = @NationalRegistrationMunicipalityCode, CitizenshipCode = @CitizenshipCode, LastChangedDate = @LastChangedDate WHERE PersonalIdentityNumber = @PersonalIdentityNumber", connection);

                for (int i = 0; i < PersonalIdentityNumber.Count; i++)
                {

                    var personnummer = PersonalIdentityNumber[i];
                    var fornamn = FirstName[i];
                    var efternamn = LastName[i];
                    var lankod = LanKod[i];
                    var kommunkod = Kommunkod[i];
                    var utdelAdress2 = UtdelAdress2[i];
                    var postNr = PostNr[i];
                    //var postOrt = PostOrt[i];
                    //var fodelselanKod = FodelselanKod[i];
                    //var fodelseforsamling = Fodelseforsamling[i];
                    var medborgarskapslandKod = MedborgarskapslandKod[i];
                    // var medborgarskapsdatum = Medborgarskapsdatum[i];


                    command1.Parameters.Clear();
                    command1.Parameters.AddWithValue("@PersonalIdentityNumber", personnummer);
                    command1.Parameters.AddWithValue("@FirstName", fornamn);
                    command1.Parameters.AddWithValue("@LastName", efternamn);
                    command1.Parameters.AddWithValue("@NationalRegistrationCountyCode", lankod);
                    command1.Parameters.AddWithValue("@NationalRegistrationMunicipalityCode", kommunkod);
                    command1.Parameters.AddWithValue("@NationalRegistrationDistributionAddress2", utdelAdress2);
                    //command1.Parameters.AddWithValue("@NationalRegistrationPostCode", postNr);
                    //command1.Parameters.AddWithValue("@NationalRegistrationCity", postOrt);
                    //command1.Parameters.AddWithValue("@BirthCountyCode", fodelselanKod);
                    //command1.Parameters.AddWithValue("@BirthParish", fodelseforsamling);
                    command1.Parameters.AddWithValue("@CitizenshipCode", medborgarskapslandKod);
                    // command1.Parameters.AddWithValue("@CitizenshipDate", medborgarskapsdatum);
                    command1.Parameters.AddWithValue("@LastChangedDate", datum);



                    command1.ExecuteNonQuery();

                    Console.WriteLine(personnummer);


                }
            }

            Console.WriteLine("Done");
        }

            //}// Put a break-point here, then mouse-over PersonalIdentityNumber...  deserializedList contains everything if you need it
        //   catch (Exception)
        //    {

        //        throw;
        //    }
        //    Console.ReadKey();
        //}

    private static T Deserialize<T>() where T : new()
    {
        // Create an instance of T
        T ReturnListOfT = CreateInstance<T>();


        // Create a new file stream for reading the XML file
        using (FileStream ReadFileStream = new FileStream("navetout.xml", FileMode.Open, FileAccess.Read, FileShare.Read))
        {
            // Construct a XmlSerializer and use it  
            // to serialize the data from the stream.
            XmlSerializer SerializerObj = new XmlSerializer(typeof(T));
            try
            {
                // Deserialize the hashtable from the file
                ReturnListOfT = (T)SerializerObj.Deserialize(ReadFileStream);
            }
            catch (Exception ex)
            {
                Console.WriteLine(string.Format("Failed to serialize. Reason: {0}", ex.Message));
            }

        }
        // return the Deserialized data.
        return ReturnListOfT;
    }

    // function to create instance of T
    public static T CreateInstance<T>() where T : new()
    {
        return (T)Activator.CreateInstance(typeof(T));
    }

Answer 1

I solved it by doing this:

var PostNr = deserializedList.Where(item => item.Personpost.Adresser.Folkbokforingsadress != null).Select(item2 => item2.Personpost.Adresser.Folkbokforingsadress.PostNr).ToList();

Answer 2

Starting with C# 6.0 you can use the null-conditional-operator like this:

var PostNr = deserializedList.Select(item => item?.Personpost?.Adresser?.Folkbokforingsadress?.PostNr).ToList();

The operator works like this:

var result = x?.Y

This will return null when x is null. Otherwise it will return the value of x.Y

Answer 3

If you're using C# 6, you can use the new ?. operator:

var PostNr =
    deserializedList
        .Select(item => item.Personpost.Adresser.Folkbokforingsadress?.PostNr)
        .ToList();