AttributeError when SQLAlchemyDatastore.exclude_pks=False

[Álvaro]

When the exclude_pks parameter is set to False in datastore.sqlalchemy.SQLAlchemyDatastore the following exception is thrown:

  File "(...)python2.7/site-packages/flask_admin/datastore/sqlalchemy.py", line 250, in convert
    not callable(default_value.arg):
AttributeError: 'Sequence' object has no attribute 'arg'

The Column is defined as follows:

pk = Column(Integer, Sequence('hash_pk'), primary_key=True)