connect-mongodb default dbname is invalid.

app.js

var connect = require('connect')
  , Db = require('mongodb').Db
  , Server = require('mongodb').Server
  , server_config = new Server('localhost', 27017, {auto_reconnect: true, native_parser: true})
  , mongoStore = require('connect-mongodb');

var connect = connect.createServer(
    connect.bodyParser(),
    connect.cookieParser(),
    connect.session({
        cookie: { maxAge: 60000 * 20 } // 20 minutes
        , secret: 'foo'
        , store: new mongoStore({ server_config: server_config })
    }),
    function (req, res) {
        if (req.session) {
            var bar = req.session.bar || 0;
            req.session.bar = bar + 1;
            console.log(bar);
        }
        res.end();
    }
);
connect.listen(3000);

mongodb.log

Sun Jul 24 22:42:30 [initandlisten] connection accepted from 127.0.0.1:62969 #1
Sun Jul 24 22:42:30 [conn1] User Assertion: 13280:invalid db name: /dev.sessions
Sun Jul 24 22:42:30 [conn1] assertion 13280 invalid db name: /dev.sessions ns:/dev.sessions query:{ query: { _id: "0JCo3omFFq5LYs8d5UBrXfxi.8VQPI67lRRymPS7J+E4TNVGqgXKaKDTgc2TQ6+OrGLU" } }
Sun Jul 24 22:42:30 [conn1]  ntoskip:0 ntoreturn:1
Sun Jul 24 22:42:30 [conn1] query /dev.sessions ntoreturn:1 exception  0ms
Sun Jul 24 22:42:30 [conn1] User Assertion: 13280:invalid db name: /dev.sessions
Sun Jul 24 22:42:30 [conn1] update /dev.sessions  query: { _id: "RO6sxb26hD3oIgVkPJ7ePNx8.co1jzTFapNM2k1BmObfgGGl80bJxtwtjtupJ090Smd0" } exception 13280 invalid db name: /dev.sessions 0ms