* 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
if (owner_window)
      SetOwnerWindow(owner_window);
  }
  Init(isolate);
  AttachAsUserData(web_contents);
}
WebContents::~WebContents() {
  
  if (managed_web_contents()) {
    
    
    if (type_ == WEB_VIEW)
      guest_delegate_->Destroy();
    RenderViewDeleted(web_contents()->GetRenderViewHost());
    if (type_ == WEB_VIEW) {
      DestroyWebContents(false );
    } else {
      if (type_ == BROWSER_WINDOW && owner_window()) {
        owner_window()->CloseContents(nullptr);
      } else {
        DestroyWebContents(true );
      }
      
      
      
      WebContentsDestroyed();
    }
  }
}
void WebContents::DestroyWebContents(bool async) {