code: public static String average(String... values) {
          if (values != null) {
              return divide(sum(values), values.length + "");
          }
          return null;
      }
docs: Get the average of all input numbers. When the result is indivisible, the
  scale will depends on the scale of all input numbers
  
  Any numeric string recognized by {@code BigDecimal} is supported.
  
  @param values one or more valid number strings
  
  @return <code>(values[0] + values[1] + ...) / values.length</code>
  
  @see BigDecimal