Getting an error: Object reference not set to an instance of an object

This is my C# code.

public class Person
{
    public List<Employee> empDetails;        
}


public class Employee
{
   public string Id { get; set; }
   public string Name { get; set; }
   public string proj { get; set; }
   public string No { get; set; }
}
//This method is defined in a service
    public void ReadFiles()
    {
        DirectoryInfo dir = new DirectoryInfo("E:/NewFolder/NewFiles");
        FileInfo[] files = dir.GetFiles("*.*");
        Person p = 开发者_StackOverflow中文版new Person();
        Employee e = new Employee();
        foreach (FileInfo f in files)
        {
            XmlDocument doc = new XmlDocument();
            doc.Load(f.FullName);
            e.empId = doc.GetElementsByTagName("Id")[0].InnerText;
            e.empName = doc.GetElementsByTagName("Name")[0].InnerText;
            e.empSeatNo = doc.GetElementsByTagName("No")[0].InnerText;
            e.projGroup = doc.GetElementsByTagName("Grp")[0].InnerText;               
            p.empDetails.Add(e); //Here I get the error "Object reference not set to an instance of an object"
        }          
        }

Any helps appreciated.

The Person class does not initialise empDetails. Most people will do this in the constructor.

public class Person
{
   public Person()
   {
       empDetails = new List<Employee>();
   }

  public List<Employee> empDetails { get; private set; }
}

Also your case for the property names does not follow convention. Normaly it would EmpDetails or even better EmployeeDetails.

The list is never assigned; this should work:

public class Person
{
    private readonly List<Employee> empDetails = new List<Employee>();
    public List<Employee> EmploymentDetails { get { return empDetails; } }
}

(and access .EmploymentDetails, i.e. p.EmploymentDetails.Add(e);)