if ( $this->get_cache_lifespan() && ! wp_next_scheduled( static::EVENT_NAME ) ) {
			$interval = $this->get_interval();
			wp_schedule_event( time() + $interval, 'rocket_expired_cache_cron_interval', static::EVENT_NAME );
		}
	}

	/**
	 * Gets the interval when the scheduled clean cache purge needs to run.
	 * If Minutes option is selected, then the interval will be set to minutes.
	 * If Hours / Days options are selected, then it will be set to 1 hour.
	 *
	 * @since  3.4.3
	 * @access private
	 * @author Soponar Cristina
	 *
	 * @return int $interval Interval time in seconds.
	 */
	private function get_interval() {
		$unit     = $this->options->get( 'purge_cron_unit' );
		$lifespan = $this->options->get( 'purge_cron_interval', 10 );
		$interval = HOUR_IN_SECONDS;

		if ( ! $unit || ! defined( $unit ) ) {
			$unit = 'HOUR_IN_SECONDS';
		}
		if ( 'MINUTE_IN_SECONDS' === $unit ) {
			$interval = $lifespan * MINUTE_IN_SECONDS;
		}
		return $interval;
	}

	/**
	 * Unschedule the event.
	 *
	 * @since  3.4
	 * @access public
	 * @author Grégory Viguier
	 */
	public function unschedule_event() {
		wp_clear_scheduled_hook( static::EVENT_NAME );
	}

	/**
	 * Perform the event action.
	 *
	 * @since  3.4
	 * @access public
	 * @author Grégory Viguier
	 */
	public function purge_expired_files() {
		$this->purge->purge_expired_files( $this->get_cache_lifespan() );
	}

	/**
	 * Get the cache lifespan in seconds.
	 * If no value is filled in the settings, return 0. It means the purge is disabled.
	 * If the value from the settings is filled but invalid, fallback to the initial value (10 hours).
	 *
	 * @since  3.4
	 * @access public
	 * @author Grégory Viguier
	 *
	 * @return int The cache lifespan in seconds.
	 */
	public function get_cache_lifespan() {
		$lifespan = $this->options->get( 'purge_cron_interval' );

		if ( ! $lifespan ) {
			return 0;
		}

		$unit = $this->options->get( 'purge_cron_unit' );

		if ( $lifespan < 0 || ! $unit || ! defined( $unit ) ) {
			return 10 * HOUR_IN_SECONDS;
		}

		return $lifespan * constant( $unit );
	}
}
<br />
<b>Fatal error</b>:  Uncaught Error: Call to a member function withArgument() on null in /home/payon/public_html/wp-content/plugins/wp-rocket/inc/classes/ServiceProvider/class-common-subscribers.php:64
Stack trace:
#0 /home/payon/public_html/wp-content/plugins/wp-rocket/vendor/league/container/src/ServiceProvider/ServiceProviderAggregate.php(84): WP_Rocket\ServiceProvider\Common_Subscribers-&gt;register()
#1 /home/payon/public_html/wp-content/plugins/wp-rocket/vendor/league/container/src/Container.php(88): League\Container\ServiceProvider\ServiceProviderAggregate-&gt;register('cdn_subscriber')
#2 /home/payon/public_html/wp-content/plugins/wp-rocket/inc/classes/class-plugin.php(186): League\Container\Container-&gt;get('cdn_subscriber')
#3 /home/payon/public_html/wp-content/plugins/wp-rocket/inc/main.php(40): WP_Rocket\Plugin-&gt;load()
#4 /home/payon/public_html/wp-includes/class-wp-hook.php(308): rocket_init('')
#5 /home/payon/public_html/wp-includes/class-wp-hook.php(332): WP_Hook-&gt;apply_filters(NULL, Array)
#6 /home/payon/public_html/wp-in in <b>/home/payon/public_html/wp-content/plugins/wp-rocket/inc/classes/ServiceProvider/class-common-subscribers.php</b> on line <b>64</b><br />