Fix UserProfile->getUserId() unable to return null

Author: carlbennett

src/Libraries/UserProfile.php

@@ -290,7 +290,7 @@ public function getUser(): ?User
     return is_null($this->user_id) ? null : new User($this->user_id);
   }
 
-  public function getUserId(): int
+  public function getUserId(): ?int
   {
     return $this->user_id;
   }