docs: public void incrementAll(CounterMap<F, S> other) {
          for (Map.Entry<F, Counter<S>> entry : other.maps.entrySet()) {
              F key = entry.getKey();
              Counter<S> innerCounter = entry.getValue();
              for (Map.Entry<S, AtomicDouble> innerEntry : innerCounter.entrySet()) {
                  S value = innerEntry.getKey();
                  incrementCount(key, value, innerEntry.getValue().get());
              }
          }
      }