css/css-images/image-set/image-set-empty-url-rendering.html

<!DOCTYPE html>
<title>Image set empty url rendering</title>
<link rel="author" title="Noam Rosenthal" href="mailto:noam@webkit.org">
<link rel="author" title="Traian Captan" href="mailto:tcaptan@chromium.org">
<link rel="help" href="https://drafts.csswg.org/css-images-4/#image-set-notation">
<link rel="match" href="reference/image-set-rendering-ref.html">
<meta name="assert" content="image-set rendering when 2x url is empty">
<style>
  #test {
    background-image: image-set(
      url("/images/green.png") 1x,
      url("") 2x
    );
    width: 100px;
    height: 100px;
  }
</style>
<div id="test"></div>