Symlink created with external volume

Docker version: Docker version 17.06.0-ce, build 02c1d8
Compose version: docker-compose version 1.14.0, build c7bdf9e

So I have the following docker-compose file to run NGINX:

version: "3.0"
      - 80:80
      - ./prod/nginx.conf:/etc/nginx/nginx.conf:ro
      - nginx_logs:/var/log/nginx:rw
      - /data/thumbs:/thumbs:ro
     external: true

I created the nginx_logs volume by running docker volume create --name=nginx_logs

Now, I tried to access the logs from an other container (filebeat here) running:

docker run \
       --name filebeat \
       -v nginx_logs:/var/log \
       -it filebeat /bin/bash

However when running ls -l /var/log in the filebeat docker I clearly see 2 log files, but with a symlink attached to it:

/var/log/access.log -> /dev/stdout
/var/log/error.log -> /dev/stdout

Why is a symlink created ?
If I remove the file and run touch /var/log/access.log, I can read the file but not with the symlink.
Any idea how to avoid having to run the touch command ?

On NGINX containers all errors and logs has these symlinks in order to pass all outputs to container output logs, which means everything you set to /dev/stdout will be show when you run:

docker logs nginx