Codegen silently skips some getters

Given data object:

```
@DataObject(generateConverter=true)
public class MyDo {
private Map> data;
... JsonObject ctor, toJson, getter/setter
}
```

The converter generated for it silently skips the `Map> getData()` method conversion, does not throw errors during build.

To me, this did not occur at all when service (that defines API using MyDo) used locally, all worked just fine. But once used remotely (via ProxyHelper.registerService), things suddenly broke naturally, as data was simply missing when sent over wire.

Is this intentional? As I got really puzzled where the data goes away?

Start by tracing converter generation for the MyDo.getData() getter and reproduce the nested Map> case described in the issue. Compare local calls with the remote path through ProxyHelper.registerService and determine whether the missing field is an intentional limitation or a conversion bug; done means the behavior is documented or the getter is converted consistently.

Written by the indexing model from the issue text.