Returns true if a BreakdownSet contains no entries. If there are Breakdowns in the list but they do not contain values this function will return true. This is a useful function when developing new KPI formula as it can be used for simple debug logging.
var issues = metrics.get('critical issues').getLatest();
if (issues.breakdown().isNull()){
console.log('No breakdown values for critical issues on: %s',
now);
}