I have a form with a drop down field that its fill by a lookup rule, when there is data on the DB about this field it works as expected, but if there is  not data about that particular field on the DB, the drop down field its in blank and user can´t select any of the options on the field.

In our case the db may or may not contain data, but in the case on the db are no data the user most have the capacity to select one of the options on the menu.