Error while user try to login via poulpe

Precondition:
1. User with same credentials must exist in JC database and in poulpe database.
2. When user try to login via JC (authenticateDefault method) NotFoundException or AuthenticationException should be thrown
3. User logged off
4. Poulpe Auth Plugin should be enabled
Steps to reproduce:
1. Click "Sign in" button
2. Type credentials
3. Click "Sign in"

Actual result: Message "Server encounters an error while processing your request"
Expected result: User logged in