A non-numeric value encountered in picture_background_formatter_generate_background_css() line 143

Problem/Motivation

Line 143 is trying to multiply the $multiplier * 96, the multiplier is not numeric, needs to be cast into an int.

$css .= '@media (-webkit-min-device-pixel-ratio: ' . $multiplier . '), (min-resolution: ' . $multiplier * 96 . 'dpi), (min-resolution: ' . $multiplier . 'dppx) {';

Proposed resolution

cast $multiplier into int where the issue is occurring.