test media-tag, and fix the bug the tests exposed

www/assert/main.js

@@ -9,7 +9,8 @@ define([
     '/common/common-thumbnail.js',
     '/common/wire.js',
     '/common/flat-dom.js',
-], function ($, Hyperjson, Sortify, Drive, Test, Hash, Util, Thumb, Wire, Flat) {
+    '/common/media-tag.js',
+], function ($, Hyperjson, Sortify, Drive, Test, Hash, Util, Thumb, Wire, Flat, MediaTag) {
     window.Hyperjson = Hyperjson;
     window.Sortify = Sortify;
 
@@ -295,6 +296,26 @@ define([
             !secret.hashData.present);
     }, "test support for ugly tracking query paramaters in url");
 
+    assert(function (cb) {
+        try {
+            MediaTag(void 0).on('progress').on('decryption');
+            return void cb(true);
+        } catch (e) {
+            console.error(e);
+            return void cb(false);
+        }
+    }, 'check that MediaTag does the right thing when passed no value');
+
+    assert(function (cb) {
+        try {
+            MediaTag(document.createElement('div')).on('progress').on('decryption');
+            return void cb(true);
+        } catch (e) {
+            console.error(e);
+            return void cb(false);
+        }
+    }, 'check that MediaTag does the right thing when passed no value');
+
     assert(function (cb) {
         // TODO
         return cb(true);

www/common/media-tag.js

@@ -326,7 +326,7 @@
         if (typeof(el) === "object" && el.jQuery) { el = el[0]; }
 
         // Abort smoothly if the element is not a media-tag
-        if (el.nodeName !== "MEDIA-TAG") {
+        if (!el || el.nodeName !== "MEDIA-TAG") {
             console.error("Not a media-tag!");
             return {
                 on: function () { return this; }