Ah sorry, mixed it up with Redis server conf. Jep in turnserver.conf, everything is commented by default so yours should be fine.
However please try to comment external-ip. Setting any IP in the config caused issues during my tests. I think this is only required, if your TURN server is directly connected to www (not behind NAT) and/or the Nextcloud server is on a different local network.
For comparison, this works in my case (TURN server + Nextcloud on same machine behind NAT) with TLS enabled:
2018-12-07 20:33:22 root@micha:/var/log# grep '^[^#[:blank:]]' /etc/turnserver.conf
tls-listening-port=5349
fingerprint
use-auth-secret
static-auth-secret=my_secret
realm=my.domain.org
total-quota=100
bps-capacity=0
stale-nonce
cert=/etc/letsencrypt/live/my.domain.org/cert.pem
pkey=/etc/letsencrypt/live/my.domain.org/privkey.pem
cipher-list="ECDH+AESGCM:DH+AESGCM:ECDH+AES256:DH+AES256:ECDH+AES128:DH+AES:ECDH+3DES:DH+3DES:RSA+AES:RSA+3DES:!ADH:!AECDH:!MD5"
dh-file=/etc/letsencrypt/live/my.domain.org/dhparams_4096.pem
no-loopback-peers
no-multicast-peers
no-tlsv1
no-tlsv1_1