hi Friends i am facing a issue in Inheritance
i have a interface called Irewhizz
interface irewhzz
{
void object save(object obj);
void object getdata(object obj);
}
i write definition in different class like
public user:irewhzz
{
public object save(object obj);
{ .......
}
public object getdata(object obj);
{ .......
}
}
this is antoher class
public client:irewhzz
{
public object save(object obj);
{ .......
}
public object getdata(object obj);
{ .......
}
}
now i have different classes like
public partial class RwUser {

    #region variables

    IRewhizzDataHelper irewhizz;
    IRewhizzRelationDataHelper irewhizzrelation;
    private string _firstName;
    private string _lastName;
    private string _middleName;
    private string _email;
    private string _website;
    private int _addressId;
    private string _city;
    private string _zipcode;
    private string _phone;
    private string _fax;
    //private string _location;
    private string _aboutMe;
    private string _username;
    private string _password;
    private string _securityQuestion;
    private string _securityQAnswer;
    private Guid _user_Id;
    private long _rwuserid;
    private byte[] _image;
    private bool _changepassword;
    private string _mobilephone;
    private int _role;
    #endregion

    //IRewhizz is the interface and its functions are implimented by UserDataHelper class
    //RwUser Class is inheriting the UserDataHelper Properties and functions.
    //Here UserDataHelper functions are called with Irewhizz Interface Object but not with the 
    //UserDataHelper class Object It will resolves the unit testing conflict.

    #region Constructors
    public RwUser()
        : this(new UserDataHelper(), new RewhizzRelationalDataHelper())
    {

    }
    public RwUser(IRewhizzDataHelper repositary, IRewhizzRelationDataHelper relationrepositary)
    {
        irewhizz = repositary;
        irewhizzrelation = relationrepositary;
    }
    #endregion

    #region Properties
    public int Role
    {
        get
        {
            return _role;
        }
        set
        {
            _role = value;
        }
    }
    public string MobilePhone
    {
        get 
        {
            return _mobilephone;
        }
        set
        {
            _mobilephone = value;
        }
    }
    public bool ChangePassword
    {
        get
        {
            return _changepassword;
        }
        set
        {
            _changepassword = value;
        }
    }
    public byte[] Image
    {
        get
        {
            return _image;
        }
        set
        {
            _image = value;
        }

    }
    public string FirstName
    {
        get
        {
            return _firstName;
        }
        set
        {
            _firstName = value;
        }
    }

    public string LastName
    {
        get
        {
            return _lastName;
        }
        set
        {
            _lastName = value;
        }
    }
    public string MiddleName
    {
        get
        {
            return _middleName;
        }
        set
        {
            _middleName = value;
        }
    }
    public string Email
    {
        get
        {
            return _email;
        }
        set
        {
            _email = value;
        }
    }
    public string Website
    {
        get
        {
            return _website;
        }
        set
        {
            _website = value;
        }
    }
    public int AddressId
    {
        get
        {
            return _addressId;
        }
        set
        {
            _addressId = value;
        }
    }
    public string City
    {
        get
        {
            return _city;
        }
        set
        {
            _city = value;
        }
    }
    public string Zipcode
    {
        get
        {
            return _zipcode;
        }
        set
        {
            _zipcode = value;
        }
    }
    public string Phone
    {
        get
        {
            return _phone;
        }
        set
        {
            _phone = value;
        }
    }
    public string Fax
    {
        get
        {
            return _fax;
        }
        set
        {
            _fax = value;
        }
    }
    //public string Location
    //{
    //    get
    //    {
    //        return _location;
    //    }
    //    set
    //    {
    //        _location = value;
    //    }
    //}
    public string AboutMe
    {
        get
        {
            return _aboutMe;
        }
        set
        {
            _aboutMe = value;
        }
    }
    public string username
    {
        get
        {
            return _username;
        }
        set
        {
            _username = value;
        }
    }
    public string password
    {
        get
        {
            return _password;
        }
        set
        {
            _password = value;
        }
    }
    public string SecurityQuestion
    {
        get
        {
            return _securityQuestion;
        }
        set
        {
            _securityQuestion = value;
        }
    }
    public string SecurityQAnswer
    {
        get
        {
            return _securityQAnswer;
        }
        set
        {
            _securityQAnswer = value;
        }
    }
    public Guid UserID
    {
        get
        {
            return _user_Id;
        }
        set
        {
            _user_Id = value;
        }
    }
    public long RwUserID
    {
        get
        {
            return _rwuserid;
        }
        set
        {
            _rwuserid = value;
        }
    }
    #endregion


    #region MemberFunctions
    // DataHelperDataContext db = new DataHelperDataContext();
    // RewhizzDataHelper rwdh=new RewhizzDataHelper();

    //It saves user information entered by user and returns the id of that user 
    public object saveUserInfo(RwUser userObj)
    {

        userObj.UserID = irewhizzrelation.GetUserId(username);
        var res = irewhizz.saveData(userObj);
        return res;
    }

    //It returns the security questions for user registration


}

public class Agent : RwUser { IRewhizzDataHelper irewhizz; IRewhizzRelationDataHelper irewhizzrelation; private int _roleid; private int _speclisationid; private int[] _language; private string _brokaragecompany; private int _loctionType_lk; private string _rolename; private int[] _specialization; private string _agentID; private string _expDate; private string _regstates; private string _selLangs; private string _selSpels; private string _locations; public string Locations { get { return _locations; } set { _locations = value; } } public string SelectedLanguages { get { return _selLangs; } set { _selLangs = value; } } public string SelectedSpecialization { get { return _selSpels; } set { _selSpels = value; } } public string RegisteredStates { get { return _regstates;

        }
        set
        {
            _regstates = value;
        }
    }

    //private string _registeredStates;
    public string AgentID
    {
        get
        {
            return _agentID;

        }
        set
        {
            _agentID = value;

        }
    }
    public string ExpDate
    {
        get
        {
            return _expDate;

        }
        set
        {
            _expDate = value;

        }
    }
    private int[] _registeredStates;
    public SelectList RegisterStates
    {
        set;
        get;
    }
    public SelectList Languages
    {
        set;
        get;
    }
    public SelectList Specializations
    {
        set;
        get;
    }
    public int[] RegisterdStates
    {
        get
        {
            return _registeredStates;
        }
        set
        {
            _registeredStates = value;
        }

    }

    //public string RegisterdStates
    //{
    //    get
    //    {
    //        return _registeredStates;
    //    }
    //    set
    //    {
    //        _registeredStates = value;
    //    }

    //}
    public int RoleId
    {
        get
        {
            return _roleid;
        }
        set
        {
            _roleid = value;
        }

    }
    public int SpeclisationId
    {
        get
        {
            return _speclisationid;
        }
        set
        {
            _speclisationid = value;
        }

    }
    public int[] Language
    {
        get
        {
            return _language;
        }
        set
        {
            _language = value;
        }

    }
    public int LocationTypeId
    {
        get
        {
            return _loctionType_lk;
        }
        set
        {
            _loctionType_lk = value;
        }

    }
    public string BrokarageCompany
    {
        get
        {
            return _brokaragecompany;
        }
        set
        {
            _brokaragecompany = value;
        }

    }
    public string Rolename
    {
        get
        {
            return _rolename;
        }
        set
        {
            _rolename = value;
        }

    }

    public int[] Specialization
    {
        get
        {
            return _specialization;
        }
        set
        {
            _specialization = value;
        }

    }
    public Agent()
        : this(new AgentDataHelper(), new RewhizzRelationalDataHelper())
    {

    }
    public Agent(IRewhizzDataHelper repositary, IRewhizzRelationDataHelper relationrepositary)
    {
        irewhizz = repositary;
        irewhizzrelation = relationrepositary;

    }

    public void inviteclient()
    {
        //Code related to mailing
    }

    //DataHelperDataContext dataObj = new DataHelperDataContext();

    //#region IRewhizzFactory Members


    //public List<object> getAgentInfo(string username)
    //{
    //    var res=dataObj.GetCompleteUserDetails(username);
    //    return res.ToList();

    //    throw new NotImplementedException();
    //}
    //public List<object> GetRegisterAgentData(string username)
    //{
    //   var res= dataObj.RegisteredUserdetails(username);
    //   return res.ToList();
    //}






    //public void saveAgentInfo(string username, string password, string firstname, string lastname, string middlename, string securityquestion, string securityQanswer)
    //{
    //    User userobj=new User();


    //    var result = dataObj.rw_Users_InsertUserInfo(firstname, middlename, lastname, dataObj.GetUserId(username), securityquestion, securityquestionanswer);






    //    throw new NotImplementedException();
    //}

    //#endregion

    public Agent updateData(Agent objectId)
    {

        objectId.UserID = irewhizzrelation.GetUserId(objectId.username);
        objectId = (Agent)irewhizz.updateData(objectId);
        return objectId;
    }
    public Agent GetAgentData(Agent agentodj)
    {
        agentodj.UserID = irewhizzrelation.GetUserId(agentodj.username);
        agentodj = (Agent)irewhizz.getData(agentodj);
        if (agentodj.RoleId != 0)
            agentodj.Rolename = (string)(string)irewhizzrelation.getValue(agentodj.RoleId);

        if (agentodj.RegisterdStates.Count() != 0)
        {

            List<SelectListItem> list = new List<SelectListItem>();
            string regstates = "";
            foreach (int i in agentodj.RegisterdStates)
            {
                SelectListItem listitem = new SelectListItem();
                listitem.Value = i.ToString();
                listitem.Text = (string)irewhizzrelation.getValue(i);
                list.Add(listitem);
                regstates += (string)irewhizzrelation.getValue(i) + ",";
            }
            SelectList selectlist = new SelectList(list, "Value", "Text");
            agentodj.RegisterStates = selectlist;
            if(regstates!=null)
            agentodj.RegisteredStates = regstates.Remove(regstates.Length - 1);

        }


        if (agentodj.Language.Count() != 0)
        {
            List<SelectListItem> list = new List<SelectListItem>();
            string selectedlang = "";
            foreach (int i in agentodj.Language)
            {
                SelectListItem listitem = new SelectListItem();
                listitem.Value = i.ToString();
                listitem.Text = (string)irewhizzrelation.getValue(i);
                list.Add(listitem);
                selectedlang += (string)irewhizzrelation.getValue(i) + ",";

            }
            SelectList selectlist = new SelectList(list, "Value", "Text");
            agentodj.Languages = selectlist;
            // agentodj.SelectedLanguages = selectedlang;

        }


        if (agentodj.Specialization.Count() != 0)
        {
            List<SelectListItem> list = new List<SelectListItem>();
            string selectedspel = "";
            foreach (int i in agentodj.Specialization)
            {
                SelectListItem listitem = new SelectListItem();
                listitem.Value = i.ToString();
                listitem.Text = (string)irewhizzrelation.getValue(i);
                list.Add(listitem);
                selectedspel += (string)irewhizzrelation.getValue(i) + ",";
            }
            SelectList selectlist = new SelectList(list, "Value", "Text");
            agentodj.Specializations = selectlist;
            //agentodj.SelectedSpecialization = selectedspel;


        }



        return agentodj;

    }
    public void SaveImage(byte[] pic, String username)
    {
        irewhizzrelation.SaveImage(pic, username);
    }



}

now the issue is when ever i am calling agent class it is given error like null reference exception for rwuser class

can any body give the solution thanks in advance