Optional content for enum variants?

[vadimcn]

Hi!
I need to de/serialize JSON messages such as the following:

{ ...,  "command": "cmd1", "arguments": { <command-dependent> } }

So far so good, this fits the adjacently tagged enum representation.
The wrinkle is that for some commands the arguments field may be optional. I tried modelling this as

#[serde(tag = "command", content = "arguments")]
enum Command {
    cmd1(Option<Cmd1Arguments>)
    ...
}

but Serde is not liking it and complains about "missing field `arguments`".

Any suggestions? (besides custom serialization)