OleDbReader -Object reference not set to an instance of an object

[maylortaylor]

 Function AddUsersToDictionary()
        Dim connectionString As String = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" & ConfigurationManager.AppSettings("Database")
        Dim dbConnection As OleDbConnection = New OleDbConnection(connectionString)
 
        Try
            dbConnection.Open()
            Dim queryString As String
            queryString = "SELECT DISTINCT UserName FROM [User];"
 
            Dim dbCommand As OleDbCommand = New OleDbCommand
            dbCommand.CommandText = queryString
            dbCommand.Connection = dbConnection
            'Dim dataAdapter As OleDbDataAdapter = New OleDbDataAdapter
            'dataAdapter.SelectCommand = dbCommand
            Dim rdr As OleDbDataReader = dbCommand.ExecuteReader()
            While rdr.Read()
                'If UserDictionary.ContainsKey(rdr.Item("UserName")) = False Then
                UserDictionary.Add(rdr.Item("UserName").ToString, 1)
                'End If
            End While
 
            rdr.Close()
            'Dim clientName As String
            'dbConnection.Open()
            'clientName = dbCommand.ExecuteScalar()
 
 
 
        Catch ex As Exception
            Console.WriteLine(ex.Message)
            myLogger.Log(ex.Message)
        Finally
            dbConnection.Close()
        End Try
    End Function

The "Object reference not set to an instance of an object" error happens at the

"UserDictionary.add(rdr.item("UserName"),1)"

line. Any help?