old_contents: """:mod:`cliche.credentials` --- Authentication methods
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  """
  from sqlalchemy.schema import Column, ForeignKey
  from sqlalchemy.types import BigInteger, Integer, String
  
  from .user import Credential
  
  
  __all__ = 'TwitterCredential',
  
  
  class TwitterCredential(Credential):
      """Information about Twitter User"""
  
      #: (:class:`int`) The primary key from :class:`Credential.id`.
      id = Column(Integer, ForeignKey('credential.id'), primary_key=True)
  
      #: (:class:`int`) Twitter user id
      identifier = Column(BigInteger, nullable=False, unique=True)
  
      #: (:class:`str`) The oauth token.
      token = Column(String, nullable=False)
  
      #: (:class:`str`) The oauth secret token.
      token_secret = Column(String, nullable=False)
  
      __tablename__ = 'twitter_credential'
      __mapper_args__ = {'polymorphic_identity': 'twitter'}
      __repr_columns__ = id, identifier
  
new_contents: """:mod:`cliche.credentials` --- Authentication methods
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  """
  from sqlalchemy.schema import Column, ForeignKey
  from sqlalchemy.types import BigInteger, Integer, String
  
  from .user import Credential
  
  
  __all__ = 'TwitterCredential',
  
  
  class TwitterCredential(Credential):
      """Information about Twitter User"""
  
      #: (:class:`int`) The primary key from :class:`Credential.id`.
      id = Column(Integer, ForeignKey('credential.id'), primary_key=True)
  
      #: (:class:`int`) Twitter user id
      identifier = Column(BigInteger, nullable=False, unique=True)
  
      #: (:class:`str`) The oauth token.
      token = Column(String)
  
      #: (:class:`str`) The oauth secret token.
      token_secret = Column(String)
  
      __tablename__ = 'twitter_credential'
      __mapper_args__ = {'polymorphic_identity': 'twitter'}
      __repr_columns__ = id, identifier
  
subject: remove nullable constraint