### Question:
GoogleCalendarUtils { static String formatAtendees(final List<EventAttendee> attendees) { if (attendees == null || attendees.isEmpty()) { return null; } return attendees.stream() .map(EventAttendee::getEmail) .collect(Collectors.joining(",")); } private  GoogleCalendarUtils();   }### Answer:
@Test public void shouldFormatEmptyAtendees() { assertThat(GoogleCalendarUtils.formatAtendees(Collections.emptyList())).isNull(); }
@Test public void shouldFormatNullAtendees() { assertThat(GoogleCalendarUtils.formatAtendees(null)).isNull(); }