Make error message more descriptive
Make error message more descriptive

Including the model the slot() method was called on makes it easier to
track down where the error might be coming from.

foam-framework/foam2,foam-framework/foam2,jacksonic/vjlofvhjfgm,foam-framework/foam2,foam-framework/foam2,jacksonic/vjlofvhjfgm,jacksonic/vjlofvhjfgm,foam-framework/foam2