fix

lib/Collection/NullableCollection.php

@@ -11,6 +11,7 @@ class NullableCollection extends AEntityCollection
     /**
      * @param $xmlId
      * @return NullableEntity
+     * @deprecated
      */
     public function &getByXmlId($xmlId)
     {
@@ -59,6 +60,14 @@ class NullableCollection extends AEntityCollection
         return parent::pop(); // TODO: Change the autogenerated stub
     }
 
+    /**
+     * @return NullableCollection|NullableEntity[]
+     */
+    public function filter($callback = null)
+    {
+        return parent::filter($callback); // TODO: Change the autogenerated stub
+    }
+
     /**
      * @return NullableEntity[]
      */

lib/Entity/NullableEntity.php

@@ -3,10 +3,19 @@
 namespace Bx\Nullable\Entity;
 
 use Bx\Nullable\IFields\NullableFields;
+use Bx\Nullable\Factory\NullableFactory;
 use Wt\Core\Entity\AEntity;
 
 class NullableEntity extends AEntity
 {
+    /**
+     * @return NullableFactory
+     */
+    public function getFactory()
+    {
+        return parent::getFactory(); // TODO: Change the autogenerated stub
+    }
+
     /**
      * @return NullableFields
      */