Make sure there is a loader supporting the "api_platform" type

Hi.

I have installed API Platform in my Symfony 4 project and I have this exception when I go to /api : An exception occurred in driver: could not find driver in . (which is being imported from "/var/www/html/sf4proj/config/routes/api_platform.yaml"). Make sure there is a loader supporting the "api_platform" type.

Here is a part of my composer.json :

... 
   "require": {
        "php": "^7.1.3",
        "ext-iconv": "*",
        "api-platform/api-pack": "^1.1",
        "doctrine/orm": "^2.6",
        "jms/serializer-bundle": "^2.3",
        "sensio/framework-extra-bundle": "^5.1",
        "symfony/console": "^4.0",
        "symfony/flex": "^1.0",
        "symfony/framework-bundle": "^4.0",
        "symfony/lts": "^4@dev",
        "symfony/maker-bundle": "^1.4",
        "symfony/monolog-bundle": "^3.2",
        "symfony/orm-pack": "^1.0",
        "symfony/translation": "^4.0",
        "symfony/yaml": "^4.0"
    },
...

And my /config/routes/api_platform.yaml file :

api_platform:
    resource: .
    type: api_platform
    prefix: /api

I use 3 containers : PHP-FPM 7.2.5, NginX 1.14 and Postgres 10.4.

I did not find anything on this error…