Fix possible nil

[jetersen]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

Fixes a nil error

fixes #9905

Description

to_s should convert possible nil to empty string which is good enough

[ohayon]

Thanks for this @Casz ! Great fix! 🚀

[fastlane-bot]

Hey @Casz 👋

Thank you for your contribution to fastlane and congrats on getting this pull request merged 🎉
The code change now lives in the master branch, however it wasn't released to RubyGems yet.
We usually ship about once a week, and your PR will be included in the next one.

Please let us know if this change requires an immediate release by adding a comment here 👍
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[fastlane-bot]

Congratulations! 🎉 This was released as part of fastlane 2.51.0 🚀