code: public ExpiringSet<T> buildSet() {
  		Set<T> target = (Set<T>) (handleExistEls ? Sets.<T>newHashSet() :
  				(elements instanceof Set ? elements : Sets.newHashSet(elements)));
  		
  		ExpiringSet<T> expiringSet = new ExpirationSet<T>(target, ticker.or(systemTicker()),
  				defaultExpireTime.orNull(), defaultExpireUnit.orNull());
  		
  		if (handleExistEls) {
  			expiringSet.addAll(elements);
  		}
  		
  		return expiringSet;
  	}
docs: Returns a new {@link ExpiringSet} instance