MAPG-199 fix issues found by PHPStan

src/PersistentData/PersistentDataManager.php

@@ -8,7 +8,7 @@ use MapGuesser\PersistentData\Model\Model;
 
 class PersistentDataManager
 {
-    public function selectFromDb(Select $select, string $type, bool $withRelations = false): ?Model
+    public function selectFromDb(Select $select, string $type, bool $withRelations = false)
     {
         $select = $this->createSelect($select, $type, $withRelations);
 
@@ -37,7 +37,7 @@ class PersistentDataManager
         }
     }
 
-    public function selectFromDbById($id, string $type, bool $withRelations = false): ?Model
+    public function selectFromDbById($id, string $type, bool $withRelations = false)
     {
         $select = new Select(\Container::$dbConnection);
         $select->whereId($id);