Filter/Predicate validation message are not returned when `management.server.port` is set for actuator

Describe the bug The feature added in https://github.com/spring-cloud/spring-cloud-gateway/commit/f6bfd6e474fbbc0f627d9bd6bc6c1c80c7f393c9 does not work when user sets a custom management port with management.server.port.

Sample

The test below copied from current test https://github.com/spring-cloud/spring-cloud-gateway/blob/84ddb3ed74ba1a4543cf25dd95cd914c68a536da/spring-cloud-gateway-server/src/test/java/org/springframework/cloud/gateway/actuate/GatewayControllerEndpointTests.java#L182 when run in SCG repo (main branch) fails with

java.lang.AssertionError: No value at JSON path "$.message"
  ...
Caused by: java.lang.IllegalArgumentException: json can not be null or empty

The only difference with original test is the use of management.server.port=0 to change the port and removal of unnecessary code.

package org.springframework.cloud.gateway.actuate;

import static org.springframework.boot.test.context.SpringBootTest.WebEnvironment.RANDOM_PORT;

import java.net.URI;
import java.util.Collections;

import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringBootConfiguration;
import org.springframework.boot.actuate.autoconfigure.web.server.LocalManagementPort;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.boot.web.server.LocalServerPort;
import org.springframework.cloud.gateway.handler.predicate.PredicateDefinition;
import org.springframework.cloud.gateway.route.RouteDefinition;
import org.springframework.cloud.gateway.test.PermitAllSecurityConfiguration;
import org.springframework.context.annotation.Import;
import org.springframework.http.MediaType;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.test.web.reactive.server.WebTestClient;
import org.springframework.web.reactive.function.BodyInserters;

@RunWith(SpringRunner.class)
@SpringBootTest(properties = { "management.endpoints.web.exposure.include=*",
        "spring.cloud.gateway.actuator.verbose.enabled=true",
        "management.server.port=0"
        }, webEnvironment = RANDOM_PORT)
public class GatewayControllerEndpointWithCustomManagementPortTests {

    @Autowired
    WebTestClient testClient;

    @LocalServerPort
    int port;

    @LocalManagementPort
    int managementPort;

    @Test
    public void testPostRouteWithNotExistingPredicate() {

        RouteDefinition testRouteDefinition = new RouteDefinition();
        testRouteDefinition.setUri(URI.create("http://example.org"));

        PredicateDefinition predicateDefinition = new PredicateDefinition("NotExistingPredicate=test-config");
        testRouteDefinition.setPredicates(Collections.singletonList(predicateDefinition));

        testClient.post().uri("http://localhost:" + managementPort + "/actuator/gateway/routes/test-route")
                .accept(MediaType.APPLICATION_JSON).body(BodyInserters.fromValue(testRouteDefinition)).exchange()
                .expectStatus().isBadRequest().expectBody().jsonPath("$.message")
                .isEqualTo("Invalid PredicateDefinition: [NotExistingPredicate]");
    }

    @SpringBootConfiguration
    @EnableAutoConfiguration
    @Import(PermitAllSecurityConfiguration.class)
    static class TestConfig {
    }

}

spring-cloud / spring-cloud-gateway

Filter/Predicate validation message are not returned when `management.server.port` is set for actuator #2466