emailaddress function returns blank output on all field types and contexts

The emailaddress mapping function fails to resolve on every field type, both in Xporter templates and in the Send Email post function. fullname and the bare field notation work correctly in the same contexts, so the issue is isolated to emailaddress specifically.

Steps to reproduce:

1. Create a custom field of the type User Picker (single), name it "Picker", and add it to the screens of a project.
2. Create an issue on that project and set the value of this custom field with any user.
3. Install the template from Xporter's documentation, here: https://docs.getxporter.app/rest/api/content/430305/child/attachment/att430335/download
4. Export that issue using the installed template.

Expected result:

The mappings from the template:

${fullname:Picker}
${emailaddress:Picker}

Should result in the user's name and email address, like so:

John Doe
john.doe@email.com

Actual result:

The user's name is returned, but not the email:

John Doe