fixed null data array to empty array

src/Generator/sp.php.twig

         $values = DB::select('SELECT (SELECT count(*) FROM {{ spcall }}) as count, (SELECT json_agg(q) FROM (SELECT * FROM {{ spcall }} OFFSET (:page::int * :perPage::int) LIMIT :perPage) q) as data',
             array({{ argsarray }}, ":page" => $page, ":perPage" => $perPage));
         $value = $values[0];
+        if (is_null($value->data))
+        {
+            $value->data = '[]';
+        }
         $data = LuStringUtils::convertJsonString($value->data);
         return new LuMultipleDbo($value->count, $data);
     }