protected A paramAddToList(String key, UrlValue val) {
    if (val != null) {
      return this.paramAddToList(key, val.toUrlValue());
    }
    return getInstance();
  }
Sets the value for the HTTP header field name {@link HttpHeaders#X_GOOG_MAPS_EXPERIENCE_ID}.
Passing null to this method will unset the experienceId header field.

@param experienceIds The experience IDs
src/main/java/com/google/maps/PendingResultBase.java