std::list<bsoncxx::document::element> dataFields;
    // ...
    mongocxx::cursor::iterator iter = (*current);
    bsoncxx::document::view_or_value doc(*iter);
    dataFields.push_back(doc.view()['data']);
    ++(*current);
    // ...
    for(auto data: dataFields)
    {
        if (data)
        {
            if (data.type() == bsoncxx::type::k_document)
            // everytime is ok
            {
                // ...
            }

            if (data.type() == bsoncxx::type::k_binary) 
            // sometimes throws "SIGABRT: src/bson/bson-iter.c:390 bson_iter_type(): precondition failed: iter->raw"
            {
                // ...
            }
 
        }
    }