> db.t.group({})
Wed Jan 27 21:11:30 JS Error: uncaught exception: group command failed: {
"errmsg" : "$reduce has to be set",
"ok" : 0,
"ok" : 0,
"errmsg" : "$reduce has to be set"
}

> db.t.stats()
{
"sharded" : false,
"ns" : "test.t",
"count" : 4,
"size" : 144,
"storageSize" : 1024,
"nindexes" : 1,
"ok" : 1,
"ok" : 1
}