allow form inside dialog without specified method

dialog-polyfill.js

@@ -458,8 +458,9 @@
    * and possibly sets its return value.
    */
   document.addEventListener('submit', function(ev) {
-    var method = ev.target.getAttribute('method').toLowerCase();
-    if (method != 'dialog') { return; }
+    var target = ev.target;
+    if (!target || !target.hasAttribute('method')) { return; }
+    if (target.getAttribute('method').toLowerCase() != 'dialog') { return; }
     ev.preventDefault();
 
     var dialog = findNearestDialog(/** @type {Element} */ (ev.target));

suite.js

@@ -481,6 +481,24 @@ void function() {
       assert.equal(dialog.returnValue, button.value,
           'don\'t take button textContent as value');
     });
+    test('boring form inside dialog', function() {
+      var form = document.createElement('form');
+      dialog.appendChild(form);  // don't specify method
+      form.addEventListener('submit', function(ev) {
+        ev.preventDefault();
+      });
+
+      var button = document.createElement('button');
+      button.value = 'Moot';
+      form.appendChild(button);
+
+      dialog.showModal();
+      button.focus();  // emulate user focus action
+      button.click();
+
+      assert.isTrue(dialog.open, 'non-dialog form should not close dialog')
+      assert(!dialog.returnValue);
+    });
   });
 
   suite('order', function() {