Retrieving flagged messages with webklex php-imap

Question

I 'm trying to fetch flagged mails from a specified folder. I tried:

$folder->query()->not()->unflagged()->setFetchBody(false)->leaveUnread()->get();

$folder->query()->not()->where([["UNFLAGGED"]])->leaveUnread()->get();

And some other I don't have now.

It throws me this reponse:

Too few arguments to function Webklex\PHPIMAP\Query\WhereQuery::where(), 0 passed and at least 1 expected

Also tried:

$folder->query()->flagged('Flagged')->setFetchBody(false)->leaveUnread()->get();

This throws me:

Webklex \PHPIMAP\ Exceptions\ImapServerErrorException

I also tried:

$aMessage = $folder->query()->seen()->setFetchBody(false)->leaveUnread()->get();
$aMessage = $folder->query()->unseen()->setFetchBody(false)->leaveUnread()->get();
$aMessage = $folder->query()->unflagged()->setFetchBody(false)->leaveUnread()->get();
$aMessage = $folder->query()->whereAll()->setFetchBody(false)->leaveUnread()->get();

And they work perfectly.

Any ideas why I can not retrieve flagged messages or where is my error?