SonarCloud instance reports:
 Add a "NoSuchElementException" for iteration beyond the end of the collection.

...in places like:

        @Override
        public Map.Entry<Double, Long> next() {
            return new AbstractMap.SimpleImmutableEntry<>(values[currentIndex++], 1L);
        }

        @Override
        public Map.Entry<Double, Long> next() {
            entryReturned = true;
            return new AbstractMap.SimpleImmutableEntry<>(value, 1L);
        }