code: private void format(Object[] arguments, Map<String, Object> argsMap,
                          AppendableWrapper dest, FieldPosition fp) {
          if (arguments != null && msgPattern.hasNamedArguments()) {
              throw new IllegalArgumentException(
                  "This method is not available in MessageFormat objects " +
                  "that use alphanumeric argument names.");
          }
          format(0, null, arguments, argsMap, dest, fp);
      }
docs: Internal routine used by format.
  
  @throws IllegalArgumentException if an argument in the
  <code>arguments</code> map is not of the type
  expected by the format element(s) that use it.