訪問和放置到SQL查詢內部的會話變量（NullReferenceException）錯誤

Question

我有一個問題，要訪問和放置SQL查詢中的會話變量。我得到了「NullReferenceException」錯誤。如何解決它？
mycodes

public partial class MyConferences : System.Web.UI.Page 
{ 
    protected void Page_Load(object sender, EventArgs e) 
    { 
     if(!IsPostBack) 
     { 
      BindGrid(); 
     } 
    } 

    private void BindGrid() 
    { 
     Object conference = Session["myConf"]; 
     string constr = ConfigurationManager.ConnectionStrings[0].ConnectionString; 
     using(SqlConnection con = new SqlConnection(constr)) 
     { 
      string query = "SELECT conferenceName, conferenceDate, conferencePlace, submissionDueDate, category FROM Conferences WHERE email = @email)"; 

      using(SqlCommand cmd = new SqlCommand(query)) 
      { 

       cmd.Connection = con; 
       cmd.Parameters.AddWithValue("@email", conference.ToString()); 
       con.Open(); 
       GridView1.DataSource = cmd.ExecuteReader(); 
       GridView1.DataBind(); 
       con.Close(); 
       cmd.ExecuteNonQuery(); 
      } 
     }   
    } 
} 

錯誤

Answer 1

簡而言之，Session["myConf"]是NULL值，所以你需要通過對會話值進行空校驗防範的是：

private void BindGrid() 
{ 
    if (Session["myConf"] == null) 
    { 
     return; // Or whatever you want to do. 
    } 

    Object conference = Session["myConf"]; 
    //..... 
}