TypeError: Error uploading artifact to Google Artifact Registry

[farzanhaq]

I am encountering the following error when trying to push an attestation using actions/attest-build-provenance to Google Artifact Registry:
Error: TypeError [ERR_INVALID_ARG_TYPE]: The first argument must be of type string or an instance of Buffer, ArrayBuffer, or Array or an Array-like Object. Received undefined.

I am providing the subject name, subject digest and have push to registry set to enabled.

My first thought is that the bundle here is evaluating to nil:
https://github.com/actions/attest/blob/main/src/attest.ts#L40

Any tips or suggestions on how to overcome this would be much appreciated!