Bug when importing article without ORCID

[StephDriver]

When importing an article without ORCID, the imports plugin creates a null where none should be.

To reproduce: import an article without ORCID information.

[mcbrandt13]

This same issue occurs when an email is missing as well. In jats.py where the FrozenAuthor instance is created, I've done this to work around it.

frozen_orcid=author["orcid"] or '',
frozen_email=author['email'] or ''