@Test
  void emptyFormParam() throws Exception {
    Throwable exception =
        assertThrows(
            IllegalStateException.class,
            () -> parseAndValidateMetadata(formParamsClass(), "emptyFormParam", String.class));
    assertThat(exception.getMessage()).contains("FormParam.value() was empty on parameter 0");
  }
Body type is only for the body param.
jaxrs/src/test/java/feign/jaxrs/JAXRSContractTestSupport.java