Updating a document with mongoDB and mongoHQ

I'm a little confused as far as updating a document in mongo is concerned. I'm using API calls with mongoHQ to do so. Say I have the following document:

{
  _id: "1234"
}

If I use the API call mentioned here, I am able to successfully update the document with the following PUT body:

{
    "document": {
        "$set": {
            "statistics": {
                "http://localhost:8888/": "base"
            }
        }
    }
}

the resulting document is:

{
  _id: "1234",
  statistics: {
    "http://localhost:8888/": "base"
  }
}

But if I try doing something like this:

{
    "document": {
        "$set": {
            "statistics": {
                "http://localhost:8888/": "base",
                "http://localhost:8888/robots.txt": "robots"
            }
        }
    }
}

It refuses to update. Am I missing a key aspect of document updating with mongodb??

Field names cannot contain a period (.). In the second example, the second URL contains a period (reference): robots.txt.

You'll need to encode the character before updates. (like a %2E for example).