ghostServer.restart() error

ghost-dev-config.js

var path = require('path'),
	config;

config = {

	// development environment
	development: {
		url: 'http://localhost:2368',
		database: {
			client: 'sqlite3',
			connection: {
				filename: path.join(__dirname, 'node_modules', 'ghost', 'content', 'data', 'ghost-dev.db')
			},
			debug: false
		},
		server: {
			host: '127.0.0.1',
			port: '2368'
		},
		paths: {
			contentPath: path.join(__dirname, 'node_modules', 'ghost', 'content')
		}
	}

};

module.exports = config;

gulpfile.js

var gulp = require('gulp');
var ghost = require('ghost');
var path = require('path');

gulp.task('test', function (callback) {

	ghost({
		config: path.join(__dirname, 'ghost-dev-config.js')
	})
		.then(function (ghostServer) {
			ghostServer.start();

      // Restart Ghost after a few seconds to reproduce the bug
			setTimeout(function() {

        // This rule throws the error
				ghostServer.restart();

        // // However, this does work...
				// ghostServer.stop();
				// ghostServer.start();

			}, 1000);

		});

	callback();

});

Terminal output

gulp test
[17:45:21] Using gulpfile ~/Bureaublad/dev/crosshair/http/gulpfile.js
[17:45:21] Starting 'test'...
[17:45:21] Finished 'test' after 7.07 ms
Ghost is running in development... 
Listening on 127.0.0.1:2368 
Url configured as: http://localhost:2368 
Ctrl+C to shut down
Ghost is closing connections
Unhandled rejection TypeError: rootApp.listen is not a function
    at /home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/core/server/ghost-server.js:55:39
    at Promise._execute (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/node_modules/bluebird/js/release/debuggability.js:299:9)
    at Promise._resolveFromExecutor (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/node_modules/bluebird/js/release/promise.js:481:18)
    at new Promise (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/node_modules/bluebird/js/release/promise.js:77:14)
    at GhostServer.start (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/core/server/ghost-server.js:40:12)
    at tryCatcher (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/node_modules/bluebird/js/release/util.js:16:23)
    at Promise._settlePromiseFromHandler (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/node_modules/bluebird/js/release/promise.js:510:31)
    at Promise._settlePromise (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/node_modules/bluebird/js/release/promise.js:567:18)
    at Promise._settlePromise0 (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/node_modules/bluebird/js/release/promise.js:612:10)
    at Promise._settlePromises (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/node_modules/bluebird/js/release/promise.js:691:18)
    at Async._drainQueue (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/node_modules/bluebird/js/release/async.js:138:16)
    at Async._drainQueues (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/node_modules/bluebird/js/release/async.js:148:10)
    at Immediate.Async.drainQueues (/home/bruno/Bureaublad/dev/crosshair/http/node_modules/ghost/node_modules/bluebird/js/release/async.js:17:14)
    at runCallback (timers.js:637:20)
    at tryOnImmediate (timers.js:610:5)
    at processImmediate [as _immediateCallback] (timers.js:582:5)