boolean|string The key where the cache is stored on. False if the key could not be generated.
	 */
	private function get_storage_key( $type = null, $page = 1, $html = false ) {
		$type = is_null( $type ) ? '1' : $type;

		$filename = self::STORAGE_KEY_PREFIX . md5( "{$type}_{$page}_" . home_url() ) . '.' . ( $html ? 'html' : 'xml' );

		return $filename;
	}

	/**
	 * Get cache directory.
	 *
	 * @return string
	 */
	public static function get_cache_directory() {
		$dir     = wp_upload_dir();
		$default = $dir['basedir'] . '/rank-math';

		/**
		 * Filter XML sitemap cache directory.
		 *
		 * @param string $unsigned Default cache directory
		 */
		$filtered = apply_filters( 'rank_math/sitemap/cache_directory', $default );

		if ( ! is_string( $filtered ) || '' === $filtered ) {
			$filtered = $default;
		}

		return trailingslashit( $filtered );
	}

	/**
	 * Read/Write cached files.
	 *
	 * @param  mixed  $value Pass null to get option,
	 *                       Pass false to delete option,
	 *                       Pass value to update option.
	 * @param  string $type  Sitemap type.
	 * @return mixed
	 */
	public static function cached_files( $value = null, $type = '' ) {
		if ( '' !== $type ) {
			$options           = Helper::option( 'sitemap_cache_files' );
			$options[ $value ] = $type;
			return Helper::option( 'sitemap_cache_files', $options );
		}

		return Helper::option( 'sitemap_cache_files', $value );
	}

	/**
	 * Invalidate sitemap cache.
	 *
	 * @param null|string $type The type to get the key for. Null for all caches.
	 */
	public static function invalidate_storage( $type = null ) {
		/**
		 * Filter: 'rank_math/sitemap/invalidate_storage' - Allow developers to disable sitemap cache invalidation.
		 */
		if ( ! apply_filters( 'rank_math/sitemap/invalidate_storage', true, $type ) ) {
			return;
		}

		$wp_filesystem = Helper::get_filesystem();
		if ( is_null( $wp_filesystem ) ) {
			return;
		}

		$directory = self::get_cache_directory();

		if ( is_null( $type ) ) {
			$wp_filesystem->delete( $directory, true );
			wp_mkdir_p( $directory );
			self::clear_transients();
			self::cached_files( false );
			Helper::clear_cache( 'sitemap' );
			return;
		}

		$data  = [];
		$files = self::cached_files();
		foreach ( $files as $file => $sitemap_type ) {
			if ( $type !== $sitemap_type ) {
				$data[ $file ] = $sitemap_type;
				continue;
			}

			$wp_filesystem->delete( $directory . $file );
		}

		self::clear_transients( $type );
		self::cached_files( $data );
		Helper::clear_cache( 'sitemap/' . $type );

		/**
		 * Action: 'rank_math/sitemap/invalidated_storage' - Runs after sitemap cache invalidation.
		 */
		do_action( 'rank_math/sitemap/invalidated_storage', $type );
	}

	/**
	 * Reset ALL transient caches.
	 *
	 * @param null|string $type The type to get the key for. Null for all caches.
	 */
	private static function clear_transients( $type = null ) {

		if ( is_null( $type ) ) {
			return Database::table( 'options' )
				->whereLike( 'option_name', '_transient_sitemap_' )
				->delete();
		}

		return Database::table( 'options' )
			->whereLike( 'option_name', '_transient_sitemap_' . $type )
			->delete();
	}
}
<br />
<b>Fatal error</b>:  Uncaught Error: Class 'RankMath\Sitemap\Cache' not found in /home/candoodesigncom/public_html/wp-content/plugins/seo-by-rank-math/includes/modules/sitemap/html-sitemap/class-sitemap.php:49
Stack trace:
#0 /home/candoodesigncom/public_html/wp-content/plugins/seo-by-rank-math/includes/modules/sitemap/class-sitemap.php(54): RankMath\Sitemap\Html\Sitemap-&gt;__construct()
#1 /home/candoodesigncom/public_html/wp-content/plugins/seo-by-rank-math/includes/module/class-manager.php(487): RankMath\Sitemap\Sitemap-&gt;__construct()
#2 /home/candoodesigncom/public_html/wp-content/plugins/seo-by-rank-math/includes/module/class-manager.php(467): RankMath\Module\Manager-&gt;load_module('sitemap', Object(RankMath\Module\Module))
#3 /home/candoodesigncom/public_html/wp-includes/class-wp-hook.php(324): RankMath\Module\Manager-&gt;load_modules('')
#4 /home/candoodesigncom/public_html/wp-includes/class-wp-hook.php(348): WP_Hook-&gt;apply_filters(NULL, Array)
#5 /home/candoodesigncom/public_html/wp-includes/plugin.php(517): WP_Hook-&gt;do_action(A in <b>/home/candoodesigncom/public_html/wp-content/plugins/seo-by-rank-math/includes/modules/sitemap/html-sitemap/class-sitemap.php</b> on line <b>49</b><br />