Symfony2 : Error with entitymanager configuration

Error : InvalidConfigurationException: Unrecognized options "auto_mapping" under "doctrine.orm"

This is my config.yml file code

# Doctrine Configuration
doctrine:
    dbal:
        default_connection: default
        connections:
            default:
                driver:   "%database_driver%"
                host:     "%database_host%"
                port:     "%database_port%"
                dbname:   "%database_name%"
                user:     "%database_user%"
                password: "%database_password%"
                charset:  UTF8
            symfonydb:
                driver:   pdo_mysql
                host:     localhost
                port:     null
                dbname:   symfony
                user:     root
                password: null
                charset:  UTF8
        # if using pdo_sqlite as your database driver, add the path in parameters.yml
        # e.g. database_path: "%kernel.root_dir%/data/data.db3"
        # path:     "%database_path%"

    orm:
        auto_generate_proxy_classes: "%kernel.debug%"
        auto_mapping: true
        default_entity_manager: default    <<<<<<<<<<
        entity_managers:
            default:
                connection: default
                mappings:
                    AcmeDemoBundle:  ~
                    AcmeUserBundle: ~
            symfonydb:
                connection: symfonydb
                mappings:
                    FooNewsBundle: ~    <<<<<<<<<

If I remove code which is after auto_mapping: true, then it works fine and not throw any error. So what is the problem?

Thnaks.