Trim trailing commas

[devhl-labs]

I don't see a way to trim trailing commas. I imagine it should be like this, but for it to work I need to evaluate the value prior to removing the trailing comma. Over in the OpenAPI generator, I can do {{^-last}},{{/-last}} to avoid printing the comma in the first place, but that does not work here.

.insert_fn("trim-trailing-comma", move |value| {
    if value.ends_with(',') {
        let mut chars = value.chars();
        chars.next_back();
        chars.as_str().to_string()
    } else {
        value.to_string()
    }
})