That’s something in your child theme (which is called “zeriflite_child”, as shown in the error above). The lines themselves are valid—they’re also used in the main theme—but the main theme defines the variable $zerif_lite_sidebars
properly before trying to use it.
You’d get the same error if you wrote:
if ( empty ( $ppp[ $qqq ] ) ) {
}
in your child theme’s functions.php. PHP doesn’t allow this.
So the answer is to fix your child theme so that the variable is properly defined.