Undefined index: sidebar_first sidebar_second in zurb_foundation_preprocess_page()

Got notices like

Undefined index: sidebar_first in zurb_foundation_preprocess_page()
Undefined index: sidebar_second in zurb_foundation_preprocess_page() (line 290 of zurb_foundation.theme)

I have a fix and will have a patch here. It's a simple thing. I had unset the sidebars in my child theme and got these notices.

  // Convenience variables
  $left = $variables['page']['sidebar_first'];
  $right = $variables['page']['sidebar_second'];