Author's Twitter Handle is missing

I have a multi-author blog and I filled the @username’s for each author from the Profile editor. However, When I see the tags added by SEO Ultimate in the posts’ headers, there is no twitter:creator tag. Hence, Twitter does not show it in the tweets.

When you open Open Graph Integrator tab, you can see a field for twitter:creator tag in the Sitewide tab, under the Twitter Card Tags section. But I can’t put a @username there because I have many authors.

Note:
All the other fields of the card (i.e. site’s @username, title, desc, image) are shown just fine.

Thanks,
Turki

https://wordpress.org/plugins/seo-ultimate/