android stream module lost response headers when header's value is a list

//code from WXStreamModule.java 
if (headers != null) {
  Iterator<Map.Entry<String, List<String>>> it =   headers.entrySet().iterator();
  while (it.hasNext()) {
    Map.Entry<String, List<String>> entry = it.next();
    if (entry.getValue().size() > 0) {
      simpleHeaders.put(entry.getKey() == null ? "_" : entry.getKey(),   entry.getValue().get(0));
    }
  }
}

Set-Cookie: x=1;
Set-Cookie: y=2;
......