chromium/third_party/blink/web_tests/fast/dom/createElementNS-empty-namespace.html

<p>Test that createElementNS("", ...) creates an element in null namespace. Per DOM 3 Core,</p>
<pre>In programming languages where empty strings can be differentiated from null, empty strings, when given as a namespace URI, are converted to null.</pre>
<script>
if (window.testRunner)
    testRunner.dumpAsText();

var elem = document.createElementNS("", "p");
document.write(elem.namespaceURI === null ? "PASS" : ("FAIL: '" + elem.namespaceURI + "'"));
</script>