@Test
  void headerMapUserObject() throws Exception {
    final MethodMetadata md =
        parseAndValidateMetadata(
            HeaderMapInterface.class, "headerMapUserObject", HeaderMapUserObject.class);
    assertThat(md.headerMapIndex()).isEqualTo(0);
  }
Body type is only for the body param.
core/src/test/java/feign/DefaultContractTest.java