diff --git a/lib/browser/api/browser-window.js b/lib/browser/api/browser-window.js
index 43a8b3203bd7..a2b31184dc6b 100644
--- a/lib/browser/api/browser-window.js
+++ b/lib/browser/api/browser-window.js
@@ -50,13 +50,13 @@ BrowserWindow.prototype._init = function () {
     if (!event.defaultPrevented) this.setTitle(title)
   })
 
-  // Sometimes the webContents doesn't get focus when window is shown, so we 
-  // have to force focusing on webContents in this case. The safest way is to 
-  // focus it when we first start to load URL, if we do it earlier it won't 
+  // Sometimes the webContents doesn't get focus when window is shown, so we
+  // have to force focusing on webContents in this case. The safest way is to
+  // focus it when we first start to load URL, if we do it earlier it won't
   // have effect, if we do it later we might move focus in the page.
   //
   // Though this hack is only needed on OS X when the app is launched from
-  // Finder, we still do it on all platforms in case of other bugs we don't 
+  // Finder, we still do it on all platforms in case of other bugs we don't
   // know.
   this.webContents.once('load-url', function () {
     this.focus()
@@ -79,7 +79,7 @@ BrowserWindow.prototype._init = function () {
       this.webContents.send('ELECTRON_RENDERER_WINDOW_VISIBILITY_CHANGE', isVisible ? 'visible' : 'hidden')
     }
   }
-  
+
   const visibilityEvents = ['show', 'hide', 'minimize', 'maximize', 'restore']
   for (let event of visibilityEvents) {
     this.on(event, visibilityChanged)
@@ -101,6 +101,7 @@ BrowserWindow.getFocusedWindow = () => {
   for (let window of BrowserWindow.getAllWindows()) {
     if (window.isFocused()) return window
   }
+  return null
 }
 
 BrowserWindow.fromWebContents = (webContents) => {
@@ -118,20 +119,20 @@ BrowserWindow.fromDevToolsWebContents = (webContents) => {
 // Helpers.
 
 Object.assign(BrowserWindow.prototype, {
-  loadURL () {
-    return this.webContents.loadURL.apply(this.webContents, arguments)
+  loadURL (...args) {
+    return this.webContents.loadURL.apply(this.webContents, args)
   },
-  getURL () {
+  getURL (...args) {
     return this.webContents.getURL()
   },
-  reload () {
-    return this.webContents.reload.apply(this.webContents, arguments)
+  reload (...args) {
+    return this.webContents.reload.apply(this.webContents, args)
   },
-  send () {
-    return this.webContents.send.apply(this.webContents, arguments)
+  send (...args) {
+    return this.webContents.send.apply(this.webContents, args)
   },
-  openDevTools () {
-    return this.webContents.openDevTools.apply(this.webContents, arguments)
+  openDevTools (...args) {
+    return this.webContents.openDevTools.apply(this.webContents, args)
   },
   closeDevTools () {
     return this.webContents.closeDevTools()
@@ -145,8 +146,8 @@ Object.assign(BrowserWindow.prototype, {
   toggleDevTools () {
     return this.webContents.toggleDevTools()
   },
-  inspectElement () {
-    return this.webContents.inspectElement.apply(this.webContents, arguments)
+  inspectElement (...args) {
+    return this.webContents.inspectElement.apply(this.webContents, args)
   },
   inspectServiceWorker () {
     return this.webContents.inspectServiceWorker()