You'll find my PR at https://github.com/helium/helium-wallet-rs/pull/256
I've recently been spending time working with the Helium blockchain and created a POC for generating Helium wallets and ran into this bug. It is a small fix, but at first it lead me to monkey-patch helium-proto which is a repo with Protobuff bindings. Later on I was able to resolve a duplicate dependency issue (as per the PR conversation), and this ended up pulling the latest from helium-proto's master branch, which helped resolve it quite nicely.