Mongo 2.4 $add nulls test

mongo_add_test.js

use agg_test;
test_add = function() {
  var t = db.things;
  t.drop();
  t.insert({a: 2, b: 3});

  var total1 = t.aggregate({$project:{total:{$add:["$a","$b"]}}}).result[0].total;
  print("a + b = " + total1);
  var total2 = t.aggregate({$project:{total:{$add:["$a","$b","$c"]}}}).result[0].total;
  print("a + b + c = " + total2);
  if (!(total2 == 5)) {
    print("ERROR: a + b + c should be 5")
  }
}

test_add();