@Test
  void queryMapWithNull() throws Exception {
    server.enqueue(new MockResponse());

    TestInterface api = new TestInterfaceBuilder().target("http://localhost:" + server.getPort());

    Map<String, Object> queryMap = new LinkedHashMap<>();
    queryMap.put("name", "alice");
    queryMap.put("fooKey", null);
    api.queryMap(queryMap);

    assertThat(server.takeRequest()).hasPath("/?name=alice");
  }
The type of a parameter value may not be the desired type to encode as. Prefer the interface
type.
core/src/test/java/feign/FeignTest.java