public function expandMiddlewareGroup( $group ) {
		if ( ! isset( $this->middleware_groups[ $group ] ) ) {
			throw new ConfigurationException( 'Unknown middleware group "' . $group . '" used.' );
		}

		$middleware = $this->middleware_groups[ $group ];

		if ( in_array( $group, $this->middleware_groups_with_global, true ) ) {
			$middleware = array_merge( ['global'], $middleware );
		}

		return $this->expandMiddleware( $middleware );
	}