Update index.bs

Author: lucacasonato

index.bs

@@ -8201,7 +8201,7 @@ a [=struct=] with the following [=struct/items=]:
     1.  If |V| [=is not an Object=], then
         [=JavaScript/throw=] a <l spec=ecmascript>{{TypeError}}</l>.
     1.  Let |method| be [=?=] <a abstract-op>GetMethod</a>(obj, {{%Symbol.asyncIterator%}}).
-    1.  If |method| is undefined:
+    1.  If |method| is <emu-val>undefined</emu-val>:
         1.  Set |syncMethod| to [=?=] <a abstract-op>GetMethod</a>(obj, {{%Symbol.iterator%}}).
         1.  If |syncMethod| is undefined, [=JavaScript/throw=] a <l spec=ecmascript>{{TypeError}}</l>.
         1.  Return an IDL [=async iterable=] value with [=JS async iterable/object=] set to |V|,