Class com.google.common.collect.Comparators

Added Methods
Comparator<Optional<T>> emptiesFirst(Comparator<? super T>)	Returns a comparator of Optional values which treats Optional.empty as less than all other values, and orders the rest using {@code valueComparator} on the contained value.
Comparator<Optional<T>> emptiesLast(Comparator<? super T>)	Returns a comparator of Optional values which treats Optional.empty as greater than all other values, and orders the rest using {@code valueComparator} on the contained value.