clean code with clippy

src/model/trip.rs

@@ -168,7 +168,7 @@ FROM user_trip WHERE trip_details_id = (SELECT trip_details_id FROM trip WHERE i
         trip_id: i64,
     ) -> Result<(), TripDeleteError> {
         let registered_rower = Self::get_all_rower_for_id(db, trip_id).await;
-        if registered_rower.len() > 0 {
+        if registered_rower.is_empty() {
             return Err(TripDeleteError::SomebodyAlreadyRegistered);
         }