fix

default_config.php

@@ -2,6 +2,6 @@
 
 return [
     'MainAbstractFactory' => [
-        'Bx\\Null\\Factory\\NullFactory' => ['cache' => ['hit'], 'is_collection_query' => true],
-    ]
+        'Bx\Null\Factory\NullFactory' => ['cache' => ['hit'], 'is_collection_query' => true],
+    ],
 ];

lib/factory/nullormfactory.php

@@ -31,6 +31,11 @@ class NullFactory extends AORMFactory
         return 'bx_null';
     }
 
+    public function __getCollectionClass()
+    {
+        return NullCollection::class;
+    }
+
     /**
      * @param $id
      * @return NullEntity