error handling nested checkboxes as stringarray

Hi, this issue is illustrated in http://jsfiddle.net/x6fz3mgt/ .

The expected output is:
```
{
  "items": [
    {
      "name": "",
      "types": ["dog"]
    },
    {
      "name": ""
    }
  ]
}
```

But the current output is:

```
{
  "items": [
    {
      "name": ""
    },
    {
      "types": [
        "dog"
      ],
      "name": ""
    }
  ]
}
```