fix: several bug fixes as found in logs

src/Security/Voter/AvailabilityVoter.php

@@ -36,6 +36,11 @@ class AvailabilityVoter extends Voter
 
         /** @var User $user */
         $user = $this->security->getUser();
+
+        if (null === $user) {
+            return false;
+        }
+
         $teamer = $user->getTeamer();
 
         return null === $availability->getOwner() || $teamer === $availability->getOwner();