* 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
auto browser_context = web_contents()->GetBrowserContext();
  auto download_manager =
    content::BrowserContext::GetDownloadManager(browser_context);
  download_manager->DownloadUrl(
      content::DownloadUrlParameters::CreateForWebContentsMainFrame(
          web_contents(), url));
}
GURL WebContents::GetURL() const {