code: public String getStringOf(final String param, final List<String> possibleValues) {
      checkNotNull(possibleValues);
      checkArgument(!possibleValues.isEmpty());
  
      final String value = getString(param);
  
      if (possibleValues.contains(value)) {
        return value;
      } else {
        throw new InvalidEnumeratedPropertyException(fullString(param), value, possibleValues);
      }
    }
docs: Looks up a parameter.  If the value is not in <code>possibleValues</code>, throws and
  exception.
  
  @param possibleValues May not be null. May not be empty.
  @throws InvalidEnumeratedPropertyException if the parameter value is not on the list.