t = db.mr_undef;
t.drop();

outname = "mr_undef_out";
out = db[outname];
out.drop();

t.insert({x: 0});

var m = function() {
    emit(this.mod, this.x);
};
var r = function(k, v) {
    total = 0;
    for (i in v) {
        total += v[i];
    }
    return total;
};

res = t.mapReduce(m, r, {out: outname});

assert.eq(0, out.find({_id: {$type: 6}}).itcount(), "A1");
assert.eq(1, out.find({_id: {$type: 10}}).itcount(), "A2");

x = out.findOne();
assert.eq(x, out.findOne({_id: x["_id"]}), "A3");