Panics when deriving Error for an enum with a type dictionary trait

[KSXGitHub]

Code

Repo: https://github.com/KSXGitHub/bug-report-derive-more-type-dict

use derive_more::{Display, Error};

pub trait MyTypeDict {
    type Foo;
    type Bar;
}

#[derive(Debug, Display, Error)]
pub enum MyEnum<TypeDict: MyTypeDict> {
    Foo(#[error(source)] TypeDict::Foo),
    Bar(#[error(source)] TypeDict::Bar),
}

Error

error: proc-macro derive panicked
 --> src/lib.rs:8:26
  |
8 | #[derive(Debug, Display, Error)]
  |                          ^^^^^
  |
  = help: message: expected `,`

[tyranron]

Doesn't reproduce on 1.0.0-beta.3 and master.