Fix error on getUid(null) with 0 results (#499) (#573)

Co-authored-by: Wiebe Haanstra <whaanstra@eljakim.nl>

Author: pierement

src/Connection/Protocols/ImapProtocol.php

@@ -940,7 +940,7 @@ public function getUid(?int $id = null): Response {
  $uids = $this->uid_cache;
 
  if ($id == null) {
- return Response::empty($this->debug)->setResult($uids);
+ return Response::empty($this->debug)->setResult($uids)->setCanBeEmpty(true);
  }
 
  foreach ($uids as $k => $v) {