linkHeader.addLink(null, SELF, self, null);
DateMidnight prevMonth = yearMonth.minusMonths(1);
DateMidnight nextMonth = yearMonth.plusMonths(1);
boolean hasPrev = repository.hasActivitiesByYearMonth(prevMonth.year().get(), prevMonth.monthOfYear().get());
boolean hasNext = repository.hasActivitiesByYearMonth(nextMonth.year().get(), nextMonth.monthOfYear().get());
if (hasPrev)
{
String prev = uriInfo.getBaseUriBuilder().path("activities")
.segment(String.valueOf(prevMonth.year().get()), String.valueOf(prevMonth.monthOfYear().get()))
.build().toASCIIString();