Editing dataset in UI fails if dataset's creators don't have email

[m-alisafaee]

Describe the bug
When dataset creators don't have email address (e.g. when a dataset is imported), then we cannot edit the dataset in UI. The error message says that email is missing.

Link to project
https://dev.renku.ch/projects/mohammad.alisafaee/delete-me-dataset-import-and-edit-no-email

To Reproduce
Steps to reproduce the behavior:

1. Create a project in UI
2. Import a dataset from zenodo: 10.5281/zenodo.1438326
3. Once imported, try to edit the dataset in the UI (change its keywords for example).
4. Save changes
5. See error: Our servers could not process the requested operation. The following details may help: Invalid parameter value - Email is invalid: "{'name': 'Konstantin Sering'}". A valid format is "Name <email> [affiliation]"

Additional context

• Renku core version: 2.7.0
• We can edit the same dataset in CLI