private static <K, V> Comparator<Map.Entry<K, V>> byValueOnly(Comparator<V> comparator) {
        return (a, b) -> comparator.compare(a.getValue(), b.getValue());
    }
Utility method for creating a composed comparator that begins by 
comparing the first value and if it is equal, continues to the next one.

@param <K>      the type of the key to compare
@param methods  methods for comparing the key ordered by priority
@return         a composite comparator that checks the key using the
                supplied methods in order
@throws NullPointerException if any of the provided parameters are {@code null}
common-parent/mapstream/src/main/java/com/speedment/common/mapstream/MapStream.java