code: static AttrPolling createFromString(final String str)
      throws BOSHException {
          if (str == null) {
              return null;
          } else {
              return new AttrPolling(str);
          }
      }
docs: Creates a new attribute instance from the provided String.
  
  @param str string representation of the attribute
  @return instance of the attribute for the specified string, or
  {@code null} if input string is {@code null}
  @throws BOSHException on parse or validation failure