Cannot use #[deriving(Encodable)] on unit-like struct

[andrewd18]

I have a nested data structure with a few unit-like structs as placeholders. When I tried to encode the structure, I received a "not all control paths return a value" when using #[deriving(Encodable] on said unit-like structs. Works great when I take said structs out or give them data.

Unsure if bug or feature.

extern crate serialize;
use serialize::{json};

#[deriving(Encodable)]
struct UnitLikeStruct;

fn main() {
    let to_encode_object = UnitLikeStruct;
    let encoded_str: ~str = json::Encoder::str_encode(&to_encode_object);

    println!("{}", encoded_str);
}

Using a slightly older pre-nightly on Windows 7:
C:\Program Files (x86)\Rust\bin\rustc.exe 0.11-pre-nightly (1853619 2014-04-17 01:31:27 -0700)