Raise meaningful exception if amendment doesn't have a selection.
Raise meaningful exception if amendment doesn't have a selection.

Such broken data exists due to a previous bug. This makes it easier to
detect that.

liqd/adhocracy,alkadis/vcv,alkadis/vcv,DanielNeugebauer/adhocracy,phihag/adhocracy,phihag/adhocracy,liqd/adhocracy,DanielNeugebauer/adhocracy,DanielNeugebauer/adhocracy,liqd/adhocracy,alkadis/vcv,DanielNeugebauer/adhocracy,liqd/adhocracy,alkadis/vcv,phihag/adhocracy,phihag/adhocracy,DanielNeugebauer/adhocracy,alkadis/vcv,phihag/adhocracy