control reaches end of trigger procedure without RETURN

create function duplicate_images() returns OPAQUE as'    DECLARE         myrec RECORD;    BEGIN         if TG_OP =
''INSERT''then              select * into myrec from images where page=NEW.page and
 
path=NEW.path;              if found then                   raise exception ''insert failed: duplicate record found'';
           end if;         end if;    end;
 
' language 'plpgsql';