How to create json foramt using MAP class x++ D365FO

   Map myMap;
   myMap.insert("Invoice account", "INV001");
   myMap.insert("SalesId", "SO-100-001");

     Str json = JSONSerializerExtension::serializeClass(myMap);

OutPut json:
{
  "Invoice account": "INV001",
  "SalesId" :"SO-100-001"
}