Understanding jwt_payload util method

[manjurulhoque]

Thank you for the project!

def jwt_payload(user, context=None):
    username = user.get_username()

    if hasattr(username, 'pk'):
        username = username.pk

    payload = {
        user.USERNAME_FIELD: username,
        'exp': datetime.utcnow() + jwt_settings.JWT_EXPIRATION_DELTA,
    }

It's the code snippet of the package to get jwt_payload. My understanding was get_username() will always return string as its value.

Code snippet from AbstractBaseUser class.

My question is why do we need to check the username hasattr pk? Will it return an object for some cases?