[Solved] VB.Net Error: Conversion from type DBNull to type String is not valid

error message

An exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll but was not handled in user code

Additional information: Conversion from type 'DBNull' to type 'String' is not valid.

        Public Function GetValue(ByVal id As String) As IHttpActionResult
            Dim customers As New List(Of Baladata)()
            Using conn As New SqlConnection()
                conn.ConnectionString = ConfigurationManager.ConnectionStrings("KABOJJAConnectionString").ConnectionString
                '  Using Con As New SqlConnection(conString)
                Using cmd As New SqlCommand()
                    cmd.CommandText = "SELECT * FROM Androidscores WHERE phones = @CustomerId"
                    cmd.Parameters.AddWithValue("@CustomerId", id)
                    cmd.Connection = conn
                    conn.Open()
                    Using sdr As SqlDataReader = cmd.ExecuteReader()
                        While sdr.Read()
                            customers.Add(New Baladata With {
                              .Account = sdr("Account"),
                              .Classr = sdr("Class"),
                              .Stream = sdr("Stream"),
                              .Names = sdr("Names"),
                              .Subject = sdr("Subject"),
                              .Mid = sdr("Mid"),
                              .Ends = sdr("Ends"),
                              .Grade = sdr("Grade"),
                              .Term = sdr("Term"),
                              .Years = sdr("Years"),
                              .Total = sdr("Total"),
                               .Phones = sdr("Phones")
                            })
                        End While
                    End Using
                    conn.Close()
                End Using
                Return Ok(customers)
            End Using
        End Function

        Public Class Baladata
            Public Property Account() As String
            Public Property Classr() As String
            Public Property Stream() As String
            Public Property Names() As String
            Public Property Subject() As String
            Public Property Mid() As String
            Public Property Ends() As String
            Public Property Grade() As String
            Public Property Term() As String
            Public Property Years() As String
            Public Property Total() As String
            Public Property Phones() As String
        End Class