code: protected static List<String> parseOptionalStringValues(JSONObject json, String key) {
  
          List<String> list = null;
          try {
              list = parseMandatoryStringValues(json, key);
          } catch (JSONException e) {
              LOG.info(Messages.get().getBundle().key(Messages.LOG_OPTIONAL_STRING_LIST_MISSING_1, key), e);
              return null;
          }
          return list;
      }
docs: Helper for reading an optional String value list - returning <code>null</code> if parsing fails for the whole list, otherwise just skipping unparsable entries.
  @param json The JSON object where the list should be read from.
  @param key The key of the value to read.
  @return The value from the JSON, or <code>null</code> if the value does not exist.