public static <Req extends MessagingRequest> Matcher<Req> operationEquals(String operation) {
    if (operation == null) throw new NullPointerException("operation == null");
    if (operation.isEmpty()) throw new NullPointerException("operation is empty");
    return new MessagingOperationEquals<Req>(operation);
  }
@Test void operationEquals_unmatched_null() {
    assertThat(operationEquals("send").matches(request)).isFalse();
  }