@Test
    void buildIllegalExceptionTest() {
        final ServerBuilder sb = Server.builder()
                                       .service("/", (ctx, req) -> HttpResponse.of(HttpStatus.OK))
                                       .accessLogger(host -> null);
        assertThatThrownBy(sb::build).isInstanceOf(IllegalStateException.class);
        final ServerBuilder sb2 =
                Server.builder()
                      .service("/", (ctx, req) -> HttpResponse.of(HttpStatus.OK))
                      .accessLogger(host -> {
                          if ("*.example.com".equals(host.hostnamePattern())) {
                              return null;
                          }
                          return LoggerFactory.getLogger("default");
                      })
                      .virtualHost("*.example.com").and();
        assertThatThrownBy(sb2::build).isInstanceOf(IllegalStateException.class);
    }
Makes sure that {@link ServerBuilder#build()} throws {@link IllegalStateException}
when the access logger of a {@link VirtualHost} set by a user is {@code null}.
core/src/test/java/com/linecorp/armeria/server/ServerBuilderTest.java