存储库模式中出现NullReferenceException

我使用的是Repository模式，在我的Repository.cs中，我的_dataContext对象返回null。我该怎么做才能使它不返回null？

  private BlogDataContext _dataContext;
        private readonly IDbSet<T> _dbset;
        private string[] _paths;
        public Repository(IDatabaseFactory databaseFactory)
        {
                DataContext.Database.Log = Console.Write;
                DatabaseFactory = databaseFactory;
                _dbset = DataContext.Set<T>();
        }
        protected IDatabaseFactory DatabaseFactory
        {
            get;
            private set;
        }
        protected BlogDataContext DataContext
        {
            get { return _dataContext ?? (_dataContext = DatabaseFactory.Get()); }
        }