Site.renderLinkToNextMonth (lastDayIndex, currentMonth, monthNames)
check if there are any stories in the previous month

Sourcecode in Site/renderFunctions.js:
1:   function renderLinkToNextMonth(lastDayIndex, currentMonth, monthNames) {
2:      var l = this.size();
3:      if (l == 0 || lastDayIndex == 0)
4:         return " ";
5:   
6:      var nextDay = this.get(lastDayIndex - 1);
7:      if (nextDay && nextDay.groupname > currentMonth) {
8:         var month = nextDay.groupName.toString().substring(4, 6) - 1;
9:         return Html.linkAsString({href: nextDay.href()}, monthNames[month]);
10:     } else {
11:        return " ";
12:     }
13:  }