datetime fields and properties

Question

DateTime _hiredate;
        public DateTime? hiredate
        {
            get
            {
                return _hiredate;
            }
            set
            {
                _hiredate = value;
            }
        }

Error    1    Cannot implicitly convert type 'System.DateTime?' to 'System.DateTime'. An explicit conversion exists (are you missing a cast?)    E:\aspnet\comp\Business Object\company.cs    64    29    Business Object

i am getting conversion problem please help me

thanq.