example with default R values fails with `rust_function()`

I am trying to reproduce an example from your doc https://extendr.rs/user-guide/default-args.html with `rust_function()` from the last version on rextendr 0.4.2.900 but got an error: ``` # R version 4.5.2 (2025-10-31) on Ubuntu 24.04 > rust_function('#[extendr] fn check_default(#[extendr(default = "NULL")] x: Robj) -> bool { x.is_null() }') ℹ build directory: /tmp/RtmpsaFvP6/file1aa31653369785 Error in `extract_meta()`: ! Rust code contains invalid attribute macros. • ✖ No valid `fn` or `impl` block found in the following sample: • #[extendr] Run `rlang::last_trace()` to see where the error occurred. > rlang::last_trace() <error/rextendr_error> Error in `extract_meta()`: ! Rust code contains invalid attribute macros. • ✖ No valid `fn` or `impl` block found in the following sample: • #[extendr] --- Backtrace: ▆ 1. └─rextendr::rust_function("#[extendr]\nfn check_default(#[extendr(default = \"NULL\")] x: Robj) -> bool {\n x.is_null()\n}") 2. └─rextendr::rust_source(...) 3. └─rextendr::make_module_macro(code, opts[["module_name"]]) 4. └─rextendr:::find_exports(sanitize_rust_code(lines)) 5. ├─dplyr::select(...) 6. ├─dplyr::mutate(...) 7. ├─dplyr::bind_rows(...) 8. │ └─rlang::list2(...) 9. ├─rextendr:::discard(...) 10. │ └─rextendr:::.rlang_purrr_probe(.x, .p, ...) 11. │ └─rextendr:::map_lgl(.x, .p, ...) 12. │ └─rextendr:::.rlang_purrr_map_mold(.x, .f, logical(1), ...) 13. │ └─base::vapply(.x, .f, .mold, ..., USE.NAMES = FALSE) 14. └─rextendr:::map2(start, end, function(.x, .y) extract_meta(clean_lns[.x:.y])) 15. └─base::mapply(.f, .x, .y, MoreArgs = list(...), SIMPLIFY = FALSE) 16. └─rextendr (local) `<fn>`(dots[[1L]][[1L]], dots[[2L]][[1L]]) 17. └─rextendr:::extract_meta(clean_lns[.x:.y]) Run rlang::last_trace(drop = FALSE) to see 1 hidden frame. ``` Any help?