Panic when parsing struct a(fn(mut self,));

[loiclec]

Hello,

The following code crashes:

    let x = quote! {
        struct a(fn(mut self,));
    };
    let z: Result<syn::DeriveInput, _> = syn::parse2(x);

The panic message is:

thread 'fuzz::reproduce_failure_1' panicked at 'Punctuated::push_punct: cannot push punctuation if Punctuated is empty or already has trailing punctuation', /Users/loic/.cargo/registry/src/github.com-1ecc6299db9ec823/syn-1.0.87/src/punctuated.rs:181:9

I am using syn version 1.0.87 with features "full" and "visit".