* Electron version: 1.7.5

### Expected behavior

When a theme color is no longer present the webContents did-change-theme-color event should return `null`.

### Actual behavior

The event returns `"#000000"`.

### How to reproduce

1. Log the returned color of the webContents did-change-theme-color event.
2. Go to https://electron.atom.io which has a theme color.
3. Go to https://atom.io which does not have a theme color.




atom/browser/api/atom_api_web_contents.cc
return type_;
}
bool WebContents::Equal(const WebContents* web_contents) const {
  return GetID() == web_contents->GetID();
}
void WebContents::LoadURL(const GURL& url, const mate::Dictionary& options) {
  if (!url.is_valid() || url.spec().size() > url::kMaxURLChars) {
    Emit("did-fail-load",
         static_cast<int>(net::ERR_INVALID_URL),
         net::ErrorToShortString(net::ERR_INVALID_URL),
         url.possibly_invalid_spec(),
         true);
    return;
  }
  if (guest_delegate_ && !guest_delegate_->IsAttached()) {
    return;
  }
  content::NavigationController::LoadURLParams params(url);
  GURL http_referrer;
  if (options.Get("httpReferrer", &http_referrer))
    params.referrer = content::Referrer(http_referrer.GetAsReferrer(),
                                        blink::kWebReferrerPolicyDefault);
  std::string user_agent;
  if (options.Get("userAgent", &user_agent))
    web_contents()->SetUserAgentOverride(user_agent);
  std::string extra_headers;
  if (options.Get("extraHeaders", &extra_headers))
    params.extra_headers = extra_headers;
  scoped_refptr<content::ResourceRequestBodyImpl> body;