code: public static BigDecimal sum(final Iterable<? extends Number> target) {
          Validate.notNull(target, "Cannot aggregate on null");
          Validate.containsNoNulls(target, "Cannot aggregate on iterable containing nulls");
          BigDecimal total = BigDecimal.ZERO;
          int size = 0;
          for (final Number element : target) {
              total = total.add(toBigDecimal(element));
              size++;
          }
          if (size == 0) {
              return null;
          }
          return total;
      }
docs: <p>
  Returns the sum of all the numbers contained in the provided
  iterable (e.g. a collection).
  </p>
  
  @param target the iterable containing the number objects
  @return the sum, as a BigDecimal