Extension import: type 'Null' is not a subtype of type 'String' in type cast (@license)

Brief summary

I'm following the "getting started" guide to write my own extension: https://miru.js.org/en/developer/2-extension/

When doing that, I get an error when importing the extension:

type 'Null' is not a subtype of type 'String' in type cast

Steps to reproduce

1. Create extension.js file
2. Add meta data as described on https://miru.js.org/en/developer/2-extension/#write-metadata
3. Import extension
4. Get error

It fails when loading the "license" meta tag. This is missing from the documentation.

Miru version

v1.8.1-22-g8599d0d

Device

Debian Linux

Acknowledgements

• I have searched the existing issues and this is a new ticket, NOT a duplicate or related to another open issue.
• If this is an issue with a extension, I should be opening an issue in the extension repository.