ใช้ตัวแปรarrayแล้วขึ้น error --> Object reference not set to an instance of an object.

Dim Symbol() As String
    Dim Day() As String

 Private Sub CheckCompanyNWD()
        Try
            Conn = New SqlConnection
            OpenConn()
            Dim sqlComNWD As String

            'Symbol(0) = New String("0")

            Sb.Remove(0, Sb.Length())
            Sb.Append(" SELECT * FROM Tb_Non_Wrk_Day ")
            Sb.Append(" WHERE MONTH(Nwd_Date)='" & cbomonth.SelectedIndex & "' AND YEAR(Nwd_Date)='" & cboyear.Text & "' ")
            Sb.Append(" ORDER BY Nwd_Date ")
            Dim sqlSearchNWD As String
            sqlSearchNWD = Sb.ToString()
            Dim dtSearchNWD As DataTable
            dtSearchNWD = New DataTable
            dtSearchNWD = ExecuteReaderReturnDatatTable(sqlSearchNWD)
            If dtSearchNWD.Rows.Count > 0 Then
                For a As Integer = 0 To dtSearchNWD.Rows.Count - 1
                    NWD = dtSearchNWD.Rows(a)(0).ToString
                    Symbol(a) = New String(dtSearchNWD.Rows(a)(1).ToString)
                    Day(a) = New String(NWD.Day.ToString())
                    Select Case Symbol(a)
                        Case "10"
                            Symbol(a) = New String("V")
                        Case "20"
                            Symbol(a) = New String("PH")
                        Case "30"
                            Symbol(a) = New String("PH")
                        Case Else
                    End Select
                Next
            End If

            CloseConn()
        Catch ex As Exception

        End Try
    End Sub