[BUGFIX release] Ember.String.htmlSafe() should return a instance o…

…f SafeString for `null` / `undefined`

Currently, `Ember.String.htmlSafe()` returns a just String, not HTML Safe.
We expect it is a safe string.

packages/ember-htmlbars/lib/utils/string.js

@@ -24,10 +24,8 @@ import { SafeString, escapeExpression } from 'htmlbars-util';
 */
 function htmlSafe(str) {
   if (str === null || str === undefined) {
-    return '';
-  }
-
-  if (typeof str !== 'string') {
+    str = '';
+  } else if (typeof str !== 'string') {
     str = '' + str;
   }
   return new SafeString(str);

packages/ember-htmlbars/tests/utils/string_test.js

@@ -6,13 +6,19 @@ QUnit.module('ember-htmlbars: SafeString');
 QUnit.test('htmlSafe should return an instance of SafeString', function() {
   var safeString = htmlSafe('you need to be more <b>bold</b>');
 
-  ok(safeString instanceof SafeString, 'should return SafeString');
+  ok(safeString instanceof SafeString, 'should be a SafeString');
 });
 
 QUnit.test('htmlSafe should return an empty string for null', function() {
-  equal(htmlSafe(null).toString(), '', 'should return an empty string');
+  var safeString = htmlSafe(null);
+
+  equal(safeString instanceof SafeString, true, 'should be a SafeString');
+  equal(safeString.toString(), '', 'should return an empty string');
 });
 
 QUnit.test('htmlSafe should return an empty string for undefined', function() {
-  equal(htmlSafe().toString(), '', 'should return an empty string');
+  var safeString = htmlSafe();
+
+  equal(safeString instanceof SafeString, true, 'should be a SafeString');
+  equal(safeString.toString(), '', 'should return an empty string');
 });