C# dynamically set property When Property is a class?

Hi i have a Number of Properties and My properties like

  public XYZ()
        {
            xyz = new xyz1();
            xyz2 = new xyz2();
        }
        public xyz1 xyz1 { get; set; }
        public xyz2 xyz2 { get; set; }
    }
    public class xyz1
    {
        public string fName { get; set; }
        public string lnameget; set;}
}
public class xyz2
{
    public string city { get; set; }
    public string state
}

While i am setting my property on runtime i am getting exception object reference set to null.

  XYZ model = new XYZ();
                                PropertyInfo propertyInfo = model.GetType().GetProperty("fName");
                                propertyInfo.SetValue(model, Convert.ChangeType(item.InnerText, propertyInfo.PropertyType), null);

Please help me