Visual Basic.NET - ExecuteScalar null

Dim SelectComand As New OleDb.OleDbCommand

Dim Maximo As Long

SelectComand.CommandText = "SELECT max(idPersona) as max FROM Personas"

SelectComand.Connection = gConexion

Dir RLeer As Oledb.OleDbDataReader

RLeer = SelectComand.ExecuteReader

'SI NO TRAE DATOSS

If RLeer Is Nothing Then

                Maximo = 1

            Else

                'SI HAY DATOS

                If RLeer.HasRows = True Then

                    While RLeer.Read()

                        Maximo = RLeer.GetInt32(0)

                    End While

                Else

                    Maximo = 1

                End If

            End If

endif

Dim Cm as new OledbCommand("Select max(IdPersona) from personas",gConexión)

Dim Mx as long =0

if not Cm.executeScalar = DbNull.Value then Mx=Cm.ExecuteScalar

Cm.Dispose