class DemandError(Exception):
    pass

class ModelNotExistError(Exception):
    pass

class UserError(Exception):
    pass

class UserNotExistError(UserError):
    pass

class UserPasswordError(UserError):
    pass

class ProviderError(Exception):
    pass

class ProviderNotExistError(ProviderError):
    pass

class WorkflowError(Exception):

    pass

class WorkflowExit(WorkflowError):

    pass