In the following code, what is the main issue that prevents the ParkingLot from using different parking strategies correctly?

In the following code, what is the main issue that prevents the ParkingLot from using different parking strategies correctly?

class ParkingLot {
  constructor() {
    this.strategy = null;
  }
  setStrategy(strategy) {
    this.strategy = strategy;
  }
  park(vehicle) {
    return this.strategy.findSpot(vehicle);
  }
}
const lot = new ParkingLot();
lot.park('car');