$userId is not nullable

Signed-off-by: samin-z <samin.zavarkesh@gmail.com>

Author: samin-z

lib/Helper/CircleHelper.php

@@ -129,7 +129,7 @@ public function getUserIdsInCircle(string $circleId): array {
 		}
 	}
 
-	public function circleExists(string $circleId, ?string $userId): bool {
+	public function circleExists(string $circleId, string $userId): bool {
 		if (!$this->circlesEnabled) {
 			return false;
 		}