code: public boolean containsCountry (@Nullable final String sCountry)
    {
      if (sCountry == null)
        return false;
  
      final String sValidCountry = LocaleHelper.getValidCountryCode (sCountry);
      if (sValidCountry == null)
        return false;
      return m_aRWLock.readLocked ( () -> m_aCountries.contains (sValidCountry));
    }
docs: Check if the passed country is known.
  
  @param sCountry
  The country to check. May be <code>null</code>.
  @return <code>true</code> if the passed country is contained,
  <code>false</code> otherwise.