Django social authentication issue, rest_framework_social_oauth2

Using Django Forms & APIs
1

When converting a token from VK (russian social network) to a JWT token (library rest_framework_social_oauth2, did as here), an error occures:

IntegrityError at /api/v0-1-0/auth/convert-token/
duplicate key value violates unique constraint "user_email_key"
DETAIL:  Key (email)=() already exists.

Maybe it’s because of my user model requires the “email” field?