I get the following error in apt update.
Get:3 http://ppa.launchpad.net/webupd8team/java/ubuntu trusty InRelease [15.5 kB]
Err:3 http://ppa.launchpad.net/webupd8team/java/ubuntu trusty InRelease
The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C2518248EEA14886
Hit:6 https://download.sublimetext.com apt/stable/ InRelease
Reading package lists... Done
W: GPG error: http://ppa.launchpad.net/webupd8team/java/ubuntu trusty InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C2518248EEA14886
E: The repository 'http://ppa.launchpad.net/webupd8team/java/ubuntu trusty InRelease' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.
I tried the following command to remove the repository.
sudo add-apt-repository --remove ppa:webupd8team/java
But still get the same error whenever run the apt update command. I checked the apt source and packages folders. There is nothing related to this package. Then where is this repository is referring to?