Odoo apt signatures couldn’t be verified

When updating apt on Ubuntu server, i get following error

root@ip-172-31-25-25:/home/ubuntu# apt-get update 
Hit:1 http://ap-south-1.ec2.archive.ubuntu.com/ubuntu xenial InRelease
Hit:2 http://ap-south-1.ec2.archive.ubuntu.com/ubuntu xenial-updates InRelease                                                         
Hit:3 http://ap-south-1.ec2.archive.ubuntu.com/ubuntu xenial-backports InRelease                                                       
Ign:4 http://nightly.odoo.com/9.0/nightly/deb ./ InRelease                                                       
Get:5 http://nightly.odoo.com/9.0/nightly/deb ./ Release [1186 B]                      
Get:6 http://nightly.odoo.com/9.0/nightly/deb ./ Release.gpg [819 B]
Ign:6 http://nightly.odoo.com/9.0/nightly/deb ./ Release.gpg
Get:7 http://nightly.odoo.com/9.0/nightly/deb ./ Packages [1790 B]
Hit:8 http://security.ubuntu.com/ubuntu xenial-security InRelease
Fetched 3795 B in 2s (1736 B/s)
Reading package lists... Done
W: GPG error: http://nightly.odoo.com/9.0/nightly/deb ./ Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY DEF2A2198183CBB5
W: The repository 'http://nightly.odoo.com/9.0/nightly/deb ./ Release' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
root@ip-172-31-25-25:/home/ubuntu# 

To fix, run

apt-key adv --keyserver keyserver.ubuntu.com --recv-keys DEF2A2198183CBB5