| Index: sdk/lib/_internal/compiler/implementation/lib/js_array.dart | 
| diff --git a/sdk/lib/_internal/compiler/implementation/lib/js_array.dart b/sdk/lib/_internal/compiler/implementation/lib/js_array.dart | 
| index c57c15b8b0a882dec53f5923b7145d627d61e062..b53b0be9b675c84078e45f41970f65f229b78016 100644 | 
| --- a/sdk/lib/_internal/compiler/implementation/lib/js_array.dart | 
| +++ b/sdk/lib/_internal/compiler/implementation/lib/js_array.dart | 
| @@ -96,8 +96,7 @@ class JSArray<E> extends Interceptor implements List<E>, JSIndexable { | 
| return IterableMixinWorkaround.mapList(this, f); | 
| } | 
|  | 
| -  String join([String separator]) { | 
| -    if (separator == null) separator = ""; | 
| +  String join([String separator = ""]) { | 
| var list = new List(this.length); | 
| for (int i = 0; i < this.length; i++) { | 
| list[i] = "${this[i]}"; | 
|  |