Sequelize 'where' only if req.query is defined

I want to consider the where clause only if 'req.query.p' is defined:

exports.select = function(req, res) {
        db.Pelicula
            .findAndCountAll({
                limit : req.query.limit,
                offset : req.query.offset,
                where : ["nombre = ?", req.query.p]
            })
            .success(function(resp){
                console.log(JSON.stringify(resp.rows, null, 4).bold.get);
                res.json({peliculas : resp.rows, meta : { total : resp.count}});
            });
}