nullable members weird rendering behaviour

I have the following data structures defined
```
### LocationStruct (object)
+ country: Australia (CountryStruct)
+ city: Sydney (string)
+ latitude (number, nullable)
+ longitude (number, nullable)

### CountryStruct (object)
+ name: Australia (string)
+ code (string, nullable)
```
And the use case for this data is the following
```
+ Request (application/json)
+ Attributes (LocationStruct)
```
This renders to the following JSON
```
{
"country": {
"name": "Australia",
"code": "Hello, world!"
},
"city": "Sydney",
"latitude": 1,
"longitude": 1
}
```
I was expecting code, latitude and longitude to have the value null, as a sample value was not specified for them.

However, when I change the CountryStruct to be empty. eg.
```
### CountryStruct (object)
```
The following is rendered.
```
{
"country": {},
"city": "Sydney",
"latitude": null,
"longitude": null
}
```

Fairly strange behaviour. The functionality I'm looking for is to have the value null be rendered when no sample value is given to an objects member.