conflicting server name

These are different vhosts and only included config files to nginx.conf

mar 27 18:50:02 rastel nginx[6041]: nginx: [warn] conflicting server name "" on 0.0.0.0:80, ignored
mar 27 18:50:02 rastel nginx[6044]: nginx: [warn] conflicting server name "" on 0.0.0.0:80, ignored

server {
listen 80;
root /srv/www/wataha.net;
index index.php
server_name wataha.net;
}


server {
listen 80;
root /srv/www/low-level.pl;
index index.php
server_name low-level.pl;
}

root@rastel:/etc/nginx# nginx -t
nginx: [warn] conflicting server name "" on 0.0.0.0:80, ignored
nginx: the configuration file /etc/nginx/nginx.conf syntax is ok
nginx: configuration file /etc/nginx/nginx.conf test is successful

What is wrong in here?