Null Object Pattern Implementing

Null Object Design Pattern.cs

public abstract class StaffBase
{
    public abstract string IdentityNumber { get; set; }
    public abstract string FullName { get; set; }
    public abstract string Department { get; set; }

    public abstract int EfficiencyScore();
    public abstract Dictionary<int, string> TaskStatus();

    #region Null Implementation

    private static readonly NullStaff nullStaff = new NullStaff();

    public static NullStaff Null
    {
        get { return nullStaff; }
    }

    public class NullStaff
        :StaffBase
    {
        public override string IdentityNumber
        {
            get { return String.Empty; }
            set { }
        }

        public override string FullName
        {
            get { return String.Empty; }
            set { }
        }

        public override string Department
        {
            get { return String.Empty; }
            set { }
        }

        public override int EfficiencyScore()
        {
            // No operation or behaviour
            // But you can put operations depending on your case
            return 0;
        }

        public override Dictionary<int, string> TaskStatus()
        {
            // No operation or behaviour
            // But you can put operations depending on your case
            return null;
        }
    }

    #endregion
}

public class EngineerStaff
    :StaffBase
{
    public override string IdentityNumber
    {
        get { return "G03" + System.Guid.NewGuid().ToString(); } 
        set { }
    }

    public override string FullName
    {
        get { return "David Cameron"; } 
        set { }
    }

    public override string Department
    {
        get { return "Enterprise Architect"; } 
        set { }
    }

    public override int EfficiencyScore()
    {
        return 90;
    }

    public override Dictionary<int, string> TaskStatus()
    {
        return new Dictionary<int, string>();
    }
}

public class AnalystStaff
    :StaffBase
{
    public override string IdentityNumber
    {
        get { return "G05" + System.Guid.NewGuid().ToString(); }
        set { }
    }

    public override string FullName
    {
        get { return "Imran Ozipek"; }
        set { }
    }

    public override string Department
    {
        get { return "Business Analyst"; }
        set { }
    }

    public override int EfficiencyScore()
    {
        return 80;
    }

    public override Dictionary<int, string> TaskStatus()
    {
        return new Dictionary<int, string>();
    }
}

// let'S use
 public class StaffRepository
{
    public StaffBase Find(string identityNumber) 
    {
            if (identityNumber.Contains("G05"))
                return new AnalystStaff();
            else if (identityNumber.Contains("G03"))
                return new EngineerStaff();

            return StaffBase.Null;
    }

}