Notice: Undefined index: rewrite_pattern

There is a notice after activating the plugin in Transifex Live settings page.

This is the error:
Notice: Undefined index: rewrite_pattern in /var/www/html/wp-content/plugins/transifex-live-integration/includes/admin/transifex-live-integration-admin-template.php on line 137 Call Stack #TimeMemoryFunctionLocation 10.0001381080{main}( ).../options-general.php:0 20.0001381752require_once( '/var/www/html/wp-admin/admin.php' ).../options-general.php:10 30.21826790712do_action( ).../admin.php:222 40.21826791088WP_Hook->do_action( ).../plugin.php:453 50.21826791088WP_Hook->apply_filters( ).../class-wp-hook.php:323 60.21836792216Transifex_Live_Integration_Admin::options_page( ).../class-wp-hook.php:298 70.21976819912include_once( '/var/www/html/wp-content/plugins/transifex-live-integration/includes/admin/transifex-live-integration-admin-template.php' ).../transifex-live-integration-admin.php:171 " name="transifex_live_settings[rewrite_pattern]" id="transifex_live_settings_rewrite_pattern" />
(https://www.awesomescreenshot.com/image/2460114/e6fbcb02b9fe9fb306b184bf8abe8066)