if (value == null) {
            throw new LdapConfigurationException(key + " is null.");
        }
        env.put(key, value);
    }

    protected Hashtable<String, String> createAdminEnv() {
        return createEnvironment(//
                fessConfig.getLdapInitialContextFactory(), //
                fessConfig.getLdapSecurityAuthentication(), fessConfig.getLdapProviderUrl(), //