LP #1692864: GPG error while apt-get update

**Reported in Launchpad by Clark last update 29-05-2017 06:54:27

Why does I get the GPG error when updating the sources?

apt-key adv --keyserver keys.gnupg.net --recv-keys 1C4CBDCDCD2EFD2A && printf "deb http://repo.percona.com/apt $(lsb_release -sc) main\ndeb-src http://repo.percona.com/apt $(lsb_release -sc) main\n" >> /etc/apt/sources.list && apt-get update

Get:2 http://repo.percona.com jessie/main Sources [6,863 B]
Get:3 http://repo.percona.com jessie/main amd64 Packages [21.4 kB]
Ign http://repo.percona.com jessie/main Translation-en
Fetched 44.1 kB in 2s (20.9 kB/s)
Reading package lists... Done
W: GPG error: http://repo.percona.com jessie InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 9334A25F8507EFA5