### Preflight Checklist

* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

* **Electron Version:** 6.0.0-beta.13
* **Operating System:** Windows 12

### Expected Behavior

The documentation for the App events `browser-window-created` and `web-contents-created` state that the first parameter is an `Event`. I therefore expect the first parameter to be an `Event`.

### Actual Behavior

The first parameter for both of these events is `undefined`. (The second parameter is a `BrowserWindow` and `WebContents`, respectively, as documented.)
shell/browser/api/atom_api_event.cc
#include "native_mate/dictionary.h"
#include "shell/browser/api/event_emitter.h"
#include "shell/common/node_includes.h"
namespace {
v8::Local<v8::Object> CreateWithSender(v8::Isolate* isolate,
                                       v8::Local<v8::Object> sender) {
  return mate::internal::CreateJSEvent(isolate, sender, nullptr, base::nullopt);
}
void Initialize(v8::Local<v8::Object> exports,
                v8::Local<v8::Value> unused,
                v8::Local<v8::Context> context,
                void* priv) {
  mate::Dictionary dict(context->GetIsolate(), exports);
  dict.SetMethod("createWithSender", &CreateWithSender);
}
}  
NODE_LINKED_MODULE_CONTEXT_AWARE(atom_browser_event, Initialize)