Monadic way of dealing with colour count.

ColourCountMonadic.java

private abstract Optional<Counter> fetchThisMonthCounts();
private abstract Optional<Counter> fetchPreviousMonthCounts();

public Optional<Integer> totalColour() {

    return fetchThisMonthCounts().flatMap(Counter::colour).flatMap(colour1 ->
           fetchPreviousMonthCounts().flatMap(Counter::colour).flatMap(colour2 ->
           Optional.of(colour1 + colour2)
    ));
}