Filtering a form

Question

I have a form that is fed with a query and depends on a single table, the query looks like this:

SELECT Documentación.Fecha, Documentación.Categoría, Documentación.Médico, Documentación.Paciente, Documentación.Fichero, Documentación.Fichero.FileName, Documentación.Papel
FROM Pacientes RIGHT JOIN (Médicos RIGHT JOIN (Categorías RIGHT JOIN Documentación ON Categorías.Id = Documentación.Categoría) ON Médicos.Id = Documentación.Médico) ON Pacientes.Id = Documentación.Paciente
ORDER BY Documentación.Fecha;

In the table and in the form, there is a field that contains appended files.

What I need is the code to filter the records of the form based on the record, whether or not it has an appended file, so what we are needing is invoke the filter method of the form with a sentence, but which is the sentence? I tryed these ones:

Me.Filter = [Fichero].AttachmentCount = 0

where "Fichero" is the field name which cotains the file attached

But I'm afraid this one doesn't work