code: @SuppressWarnings({"unchecked","rawtypes"})
      protected String getOptionsAsDisplayString() {
          final Class<?> clazz = getUnderlyingFieldClass();
          if (clazz == Boolean.class) {
              return String.format("%s%s, %s%s", OPTION_DOC_PREFIX, Boolean.TRUE, Boolean.FALSE, OPTION_DOC_SUFFIX);
          } else if (clazz.isEnum()) {
              final Class<? extends Enum> enumClass = (Class<? extends Enum>)clazz;
              return getEnumOptions(enumClass);
          } else {
              return "";
          }
      }
docs: Returns the list of possible options values for this argument.
  
  <p>
  Currently this only make sense with {@link Boolean} and {@link Enum}. Any other class
  will result in an empty string.
  </p>
  
  @return String representing the list of possible option values, never {@code null}.