Symfony 3 / APCu PHP7

framework:
    validation:
        cache: validator.mapping.cache.doctrine.apc
    serializer:
        cache: serializer.mapping.cache.apc

doctrine:
    orm:
        metadata_cache_driver: apcu
        result_cache_driver: apcu
        query_cache_driver: apcu

网站工作正常,但是当我发送表单时,我总是收到此错误：

[2016-06-29 09:17:12] request.CRITICAL: Uncaught PHP Exception
SymfonyComponentDebugExceptionUndefinedFunctionException:
“Attempted to call function “apc_fetch” from namespace
“DoctrineCommonCache”.” at
ROUTE_TO_PROJECT/vendor/doctrine/cache/lib/Doctrine/Common/Cache/ApcCache.php
line 41 {“exception”:”[object]
(SymfonyComponentDebugExceptionUndefinedFunctionException(code:
0): Attempted to call function ”apc_fetch” from namespace
”DoctrineCommonCache”. at
ROUTE_TO_PROJECT/vendor/doctrine/cache/lib/Doctrine/Common/Cache/ApcCache.php:41)”}
[]

这是我的作曲家：

"require": {
    "php": ">=5.5.9","symfony/symfony": "3.0.*","doctrine/orm": "^2.5","doctrine/doctrine-bundle": "^1.6","doctrine/doctrine-cache-bundle": "^1.2","symfony/swiftmailer-bundle": "^2.3","symfony/monolog-bundle": "^2.8","sensio/distribution-bundle": "^5.0","sensio/framework-extra-bundle": "^3.0.2","incenteev/composer-parameter-handler": "^2.0","knplabs/knp-paginator-bundle": "^2.5","liip/imagine-bundle": "^1.5","jms/serializer-bundle": "^1.1","symfony/assetic-bundle": "^2.8","gopay/payments-sdk-php": "^1.1","knplabs/knp-snappy-bundle": "~1.4","friendsofsymfony/user-bundle": "~2.0@dev"

为什么Symfony调用apc_fetch而不是apcu_fatch？