code: public void setCountryCode(final String code) {
          if (code.length() != 2) {
              throw new IllegalArgumentException("Argument must be a two letter country code.");
          }
          this.code = code.toUpperCase();
          this.name = null;
      }
docs: Set the two letter country code.
  
  This class does not attempt to resolve the country name from the country code.
  When the country code is set the name will become null.
  
  @param code A two letter countey code.
  @throws IllegalArgumentException if the country code is not valid.