docs: public static Optional<Double> avg (List<Object> args) {
          double sum = 0d;
          int count = 0;
          for(Object arg: args) {
              Optional<? extends Number> numberOptional = Objects.toNumber( arg );
              if(numberOptional.isPresent()) {
                  sum = sum + numberOptional.get().doubleValue();
                  count = count + 1;
              }
          }
          return  count == 0 ? Optional.<Double>empty() : Optional.of( sum / count );
      }