code: protected int readConfigFileVersion() {
          try {
              return getConfig().getInt(getConfigVersionKey(), NO_CONFIG_VERSION);
          } catch (ConversionException e) {
              logger.error("Error while getting the version of the configurations: " + e.getMessage(), e);
              return ERROR_READING_CONFIG_VERSION;
          }
      }
docs: Reads the version number from the configuration file, using the key returned by {@code getConfigVersionKey()}.
  <p>
  <strong>Note:</strong> It shouldn't be overridden in normal conditions.
  
  @return the version number read, or {@code NO_CONFIG_VERSION} if no version was found or
  {@code ERROR_READING_CONFIG_VERSION} if an error occurred while reading the version
  @see #NO_CONFIG_VERSION
  @see #ERROR_READING_CONFIG_VERSION
  @see #getConfigVersionKey()