chromium/src/third_party/blink/web_tests/http/tests/misc/post-submit-button.html

<!-- Submit input with an empty name should still be sent. -->
<form method="post" action="resources/post-echo-and-notify-done.cgi">
<input type="submit" name="submit" value="">
</form>

<script>
if (window.testRunner) {
  testRunner.dumpAsText();
  testRunner.waitUntilDone();
}
document.getElementsByName("submit")[0].click();
</script>