Update index.bs

Co-authored-by: Mattias Buelens <[email protected]>

Author: youennf

index.bs

@@ -5916,7 +5916,7 @@ The following abstract operations support the implementaiton of the
  1. If ! [$ReadableStreamDefaultControllerCanCloseOrEnqueue$](|readableController|) is false, throw
     a {{TypeError}} exception.
  1. Let |enqueueResult| be [$ReadableStreamDefaultControllerEnqueue$](|readableController|,
-    |chunk|, undefined).
+    |chunk|, « »).
  1. If |enqueueResult| is an abrupt completion,
    1. Perform ! [$TransformStreamErrorWritableAndUnblockWrite$](|stream|,
       |enqueueResult|.\[[Value]]).