枚举零指针exeption

Question

我在请求参数中使用了枚举来接受品牌价值，但这不是强制性领域。因此，我使用quired = false，但是当我传递品牌null或在参数中空的时，它给出了null-pointer异常。请告诉我如何解决此问题。

public enum Brand {
    Avis("A"),
    Budget("B"),
    Payless("P");

    private String value;

    public String getvalue() {
        return value;
    }

    Brand(String value) {
        this.value = value;
    }
}

@GetMapping("/locations") // getlocation
public ResponseEntity<?> searchlocationbyproximity(
    @RequestParam(value = "brand", required = false ) Brand brand,
    @RequestParam(value = "country_code") String country_code,
    @RequestParam(value = "postal_code", required = false) String postal_code,
    @RequestParam(value = "radius") String radius,
    @RequestParam(value = "state_code", required = false) String state_code,
    @RequestParam(value = "street_name", required = false) String street_name,
    @RequestParam(value = "city", required = false) String city,
    @RequestParam(value = "transaction_id", required = false) String transaction_id
) throws Exception {