Generate failed for Xero Accounting OpenAPI spec

Hey, thanks for the awesome tool! 💚

It seems that cargo-progenitor (as of 2f32cde, but probably all prior versions 🤷) fails to generate a crate for the Xero Accounting OpenAPI spec.

After downloading the above spec to reproduce, run:

RUST_BACKTRACE="full" cargo progenitor -i xero_accounting.yaml -o xero-client -n xero-client -v 6.3.0

The output is as follows:

gen fail: TypeError(InvalidValue)
Error: generation experienced errors

Stack backtrace:
   0: anyhow::error::<impl anyhow::Error>::msg
   1: cargo_progenitor::main
   2: std::sys::backtrace::__rust_begin_short_backtrace
   3: std::rt::lang_start::{{closure}}
   4: std::rt::lang_start_internal
   5: main
   6: __libc_start_call_main
   7: __libc_start_main_alias_2
   8: _start

There are no errors for the same spec in the Swagger editor.

Download xero_accounting.yaml and first run the reported cargo progenitor command with the same options to reproduce TypeError(InvalidValue). Trace the failing generation path to the unsupported part of the Xero Accounting OpenAPI spec; done means the command completes and generates the xero-client crate without errors.