docs: public static NumberList delta(Map<String, Object> currentMap, Map<String, Object> previousMap) {
          LinkedHashMap<String, Long> values = new LinkedHashMap<String, Long>(currentMap.size());
          if(currentMap.size() != previousMap.size()) {
              throw new IllegalArgumentException("Maps must have the same keys");
          }
          for (Entry<String, Object> k : currentMap.entrySet()) {
              Object v = k.getValue();
              Number current = getNumber(v);
              Object p = previousMap.get(k.getKey());
              Number previous = null;
              if (p == null) {
                  previous = 0;
              } else {
                  previous = getNumber(p);
              }
  
              long d = (current.longValue() - previous.longValue());
              values.put(k.getKey(), d);
          }
  
          return new NumberList(values);
      }