code: public List<String> getStringList(final String key, final String sep) {
      final String val = get(key);
      if (val == null || val.trim().length() == 0) {
        return Collections.emptyList();
      }
  
      if (containsKey(key)) {
        return Arrays.asList(val.split(sep));
      } else {
        throw new UndefinedPropertyException("Missing required property '" + key
            + "'");
      }
    }
docs: Returns a list of strings with the sep as the separator of the value