bp( $srcset_values, $extensions ) {
		if ( ! $srcset_values ) {
			return false;
		}

		if ( ! is_array( $srcset_values ) ) {
			$srcset_values = explode( ',', $srcset_values );
		}

		$has_webp = false;

		foreach ( $srcset_values as $i => $srcset_value ) {
			$srcset_value = preg_split( '/\s+/', trim( $srcset_value ) );

			if ( count( $srcset_value ) > 2 ) {
				// Not a good idea to have space characters in file name.
				$descriptor   = array_pop( $srcset_value );
				$srcset_value = [
					'url'        => implode( ' ', $srcset_value ),
					'descriptor' => $descriptor,
				];
			} else {
				$srcset_value = [
					'url'        => $srcset_value[0],
					'descriptor' => ! empty( $srcset_value[1] ) ? $srcset_value[1] : '1x',
				];
			}

			$url_webp = $this->url_to_webp( $srcset_value['url'], $extensions );

			if ( ! $url_webp ) {
				$srcset_values[ $i ] = implode( ' ', $srcset_value );
				continue;
			}

			$srcset_values[ $i ] = $url_webp . ' ' . $srcset_value['descriptor'];
			$has_webp            = true;
		}

		if ( ! $has_webp ) {
			return false;
		}

		return implode( ',', $srcset_values );
	}

	/**
	 * Get a list of URL/path associations.
	 * URLs are schema-less, starting by a double slash.
	 *
	 * @since 3.4
	 *
	 * @return array A list of URLs as keys and paths as values.
	 */
	private function get_url_to_path_associations() {
		static $list;

		if ( isset( $list ) ) {
			return $list;
		}

		$content_url = preg_replace( '@^https?:@', '', content_url( '/' ) );
		$content_dir = trailingslashit( rocket_get_constant( 'WP_CONTENT_DIR' ) );
		$list        = [ $content_url => $content_dir ];

		$upload     = wp_upload_dir();
		$upload_dir = trailingslashit( $upload['basedir'] );

		if ( strpos( $upload_dir, $content_dir ) === false ) {
			$upload_url          = preg_replace( '@^https?:@', '', trailingslashit( $upload['baseurl'] ) );
			$list[ $upload_url ] = $upload_dir;
		}

		/**
		 * Filter the list of URL/path associations.
		 * The URLs with the most levels must come first.
		 *
		 * @since 3.4
		 *
		 * @param array $list The list of URL/path associations. URLs are schema-less, starting by a double slash.
		 */
		$list = apply_filters( 'rocket_url_to_path_associations', $list );
		$list = array_filter(
			$list,
			function ( $path, $url ) {
				return $path && $url && is_string( $path ) && is_string( $url );
			},
			ARRAY_FILTER_USE_BOTH
		);

		if ( $list ) {
			$list = array_unique( $list );
		}

		return $list;
	}

	/**
	 * Get a list of plugins that serve webp images on frontend.
	 * If the CDN is used, this won't list plugins that use a technique not compatible with CDN.
	 *
	 * @since 3.4
	 *
	 * @return array The WebP plugin names.
	 */
	private function get_plugins_serving_webp() {
		$webp_plugins = $this->get_webp_plugins();

		if ( ! $webp_plugins ) {
			// Somebody probably messed up.
			return [];
		}

		$checks       = [];
		$is_using_cdn = $this->is_using_cdn();

		foreach ( $webp_plugins as $plugin ) {
			if ( $is_using_cdn && $plugin->is_serving_webp_compatible_with_cdn() ) {
				$checks[ $plugin->get_id() ] = $plugin->get_name();
			} elseif ( ! $is_using_cdn && $plugin->is_serving_webp() ) {
				$checks[ $plugin->get_id() ] = $plugin->get_name();
			}
		}

		return $checks;
	}

	/**
	 * Change Youtube thumbnail extension.
	 *
	 * @param string $extension extension from the thumbnail.
	 *
	 * @return string
	 */
	public function change_youtube_thumbnail( $extension ) {
		if ( ! $this->options_data->get( 'cache_webp', 0 ) ) {
			return $extension;
		}
		return 'webp';
	}
}
<br />
<b>Fatal error</b>:  Uncaught TypeError: Argument 1 passed to WP_Rocket\Event_Management\Event_Manager::add_subscriber() must implement interface WP_Rocket\Event_Management\Subscriber_Interface, string given, called in /home/merciket/public_html/wp-content/plugins/wp-rocket/inc/Plugin.php on line 155 and defined in /home/merciket/public_html/wp-content/plugins/wp-rocket/inc/classes/event-management/class-event-manager.php:33
Stack trace:
#0 /home/merciket/public_html/wp-content/plugins/wp-rocket/inc/Plugin.php(155): WP_Rocket\Event_Management\Event_Manager-&gt;add_subscriber('WP_Rocket\\Addon...')
#1 /home/merciket/public_html/wp-content/plugins/wp-rocket/inc/main.php(42): WP_Rocket\Plugin-&gt;load()
#2 /home/merciket/public_html/wp-includes/class-wp-hook.php(324): rocket_init('')
#3 /home/merciket/public_html/wp-includes/class-wp-hook.php(348): WP_Hook-&gt;apply_filters(NULL, Array)
#4 /home/merciket/public_html/wp-includes/plugin.php(517): WP_Hook-&gt;do_action(Array)
#5 /home/merciket/public_html/wp-settings.php(506): do_action('plugins_l in <b>/home/merciket/public_html/wp-content/plugins/wp-rocket/inc/classes/event-management/class-event-manager.php</b> on line <b>33</b><br />