How to handle null in xml and c# -2

My First question is:

Sample code is*:

<?xml version="1.0"?>
<AddressDirectory>
  <Owner>Mayank</Owner>
  <Age>24</Age>
  <Company>BIPL</Company>
  <Address>
    <HouseNo>1</HouseNo>
    <StreetName>Pitampura</StreetName>
    <City>Delhi</City>
  </Address>
  <Address> 
  </Address>
</AddressDirectory>

Let's consider that this was automatically generated xml file and in the second Address tag there is nothing. It is null.

If it was not null , we are going to make a list for address and then continue with a class declaration as below. But if we do so, because of a null address tag it gives us an error.

public class AddressDirectory
{
    public string Owner { get; set; }
    public string Age { get; set; }
    public string Company { get; set; }
    [XmlElement("Address")]
    public List<Address> addressList = new List<Address>(); 
}

public class Address
{
    public string HouseNo { get; set; }
    public string StreetName { get; set; }
    public string City { get; set; }
}

If possible I would like to add an if statement saying that

if it is null , store it as string. if it is not null , go with the list thing.

Could you please show me in code part how to do that?

Best regards

*: This code is taken from Mayank Gupta.

Real Situation is:

        <Address>
          <House No="1">
            <StreetName>Pitampura</StreetNamet>
            <City>Delhi</City>
        </Address>
        <Address>
        </Address>

My code is: (I'm using XmlSerializer to deserialize the xml file. The code shown below is in the class that i have created)

[XmlElement("Address")]
public List<Address> AddressList = new List<Address>();

public class Address
{

     [XmlElement("House")]
     public List<House> HouseList = new List<House>();

     public class House
     {
         [XmlAttribute("No")]
         public int No{ get; set; }

         [XmlElement("StreetName")]
         public string StreetName{ get; set; }

         [XmlElement("City")]
         public string City{ get; set; }
     }
}

The code shown above works great while serializing the xml file only if i manually delete all the null address tags. Unfortunately xml file is generated automatically so it is not possible to delete them. So i need to find a way both for null addresses and adresses with values.

Edited situation: REVISED

xml sample:

<?xml version="1.0"?>
<XMLCD>
 <Personnel>
  <AddressDirectory>
    <Owner>Jerry</Owner>
    <Age>29</Age>
    <Company>123</Company>
    <Address>
     <ST>
      <HouseNo>1</HouseNo>
      <StreetName>5th</StreetName>
      <Town>Elmsford</Town>
     </ST>
    </Address>
    <Address> 
    </Address>
  </AddressDirectory>
  <AddressDirectory>
      <Owner>Joe</Owner>
      <Age>24</Age>
      <Company>456</Company>
      <Address>
       <ST>
        <HouseNo>1</HouseNo>
        <StreetName>10Blvd</StreetName>
        <Town>StMichael</Town>
       </ST>
      </Address>
      <Address> 
      </Address>
  </AddressDirectory>
 </Personnel>
</XMLCD>

My code:

        OpenFileDialog ofd = new OpenFileDialog();
        opnFileName = ofd.FileName;

        XmlSerializer deserializer = new XmlSerializer(typeof(XMLCD));
        TextReader reader = new StreamReader(this.opnFileName);
        object obj = deserializer.Deserialize(reader);
        XMLCD XmlData = (XMLCD)obj;
        reader.Close();

    public class XMLCD
    {
         [XmlElement("Personnel")]
         public List<Personnel> PersonnelList = new List<Personnel>();

         public class Personnel
         {
           [XmlElement("AddressDirectory")]
           public List<AddressDirectory> AddressDirectoryList = new List<AddressDirectory>();

           public class AddressDirectory
           {
                 [XmlElement("Owner")]
                 public string Owner{ get; set; }

                 [XmlElement("Age")]
                 public string Age{ get; set; }

                 [XmlElement("Company")]
                 public string Company{ get; set; }


                 [XmlElement("Address")]
                 public List<Address> AddressList = new List<Address>();

                 public class Address
                 {
                       [XmlElement("ST")]
                       public List<ST> STList = new List<ST>();

                       public class ST
                       {
                         [XmlElement("HouseNo")]
                         public string HouseNo{ get; set; }

                         [XmlElement("StreetName")]
                         public string StreetName{ get; set; }

                         [XmlElement("Town")]
                         public string Town{ get; set; }
                }
     }
  }
}

The code above works great only for xml codes who have no null adress tags. When the xml code has null adress tags as shown above it gives an error.