Bug report: Twenty Twelve uses not existing CSS class .singular

This bug (Track #26866) of Twenty Twelve WordPress theme is related to media query, that is responsible for print view.

In style.css under @media print we find bunch of rules with the CSS class .singular. As far as I know, Twenty Twelve does not generate such body class.

Most likely the easiest way to fix this bug is to append code snippet from Twenty Fourteen theme to the function that creates extra BODY classes, generate additional CSS class .singular, that would be used to mark single posts and pages.:

if ( is_singular() && ! is_front_page() ) {
	$classes[] = 'singular';
}