Merge "Return "null" cycles for deprecated callers." into pi-dev

            @Override

            public Pair<ZonedDateTime, ZonedDateTime> next() {

                if (hasNext()) {

                    final Range<ZonedDateTime> r = it.next();

                    return Pair.create(r.getLower(), r.getUpper());

                } else {

                    return Pair.create(null, null);

                }

            }

        };

    }