apt-get update: Error 404 http://nginx.org/packages/ubuntu

I installed Nginx some months ago by using "apt-get install nginx"

Now I'm getting this when running apt-get update

Hit:1 http://archive.ubuntu.com/ubuntu bionic InRelease
Get:2 http://archive.ubuntu.com/ubuntu bionic-updates InRelease [88.7 kB]
Ign:3 http://nginx.org/packages/ubuntu 'lsb-release InRelease
Get:4 http://archive.ubuntu.com/ubuntu bionic-backports InRelease [74.6 kB]
Err:5 http://nginx.org/packages/ubuntu 'lsb-release Release
404 Not Found [IP: 62.210.92.35 80]
Get:6 http://archive.ubuntu.com/ubuntu bionic-security InRelease [88.7 kB]
Get:7 http://archive.ubuntu.com/ubuntu bionic-security/main amd64 Packages [593 kB]
Get:8 http://archive.ubuntu.com/ubuntu bionic-security/main Translation-en [194 kB]
Get:9 http://archive.ubuntu.com/ubuntu bionic-security/restricted amd64 Packages [15.1 kB]
Get:10 http://archive.ubuntu.com/ubuntu bionic-security/restricted Translation-en [4,684 B]
Reading package lists... Done
E: The repository 'http://nginx.org/packages/ubuntu 'lsb-release Release' does not have a Release file.
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.

my /etc/apt/sources.list file contains

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://archive.ubuntu.com/ubuntu bionic main restricted
# deb-src http://archive.ubuntu.com/ubuntu bionic main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://archive.ubuntu.com/ubuntu bionic-updates main restricted
# deb-src http://archive.ubuntu.com/ubuntu bionic-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://archive.ubuntu.com/ubuntu bionic universe
# deb-src http://archive.ubuntu.com/ubuntu bionic universe
deb http://archive.ubuntu.com/ubuntu bionic-updates universe
# deb-src http://archive.ubuntu.com/ubuntu bionic-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://archive.ubuntu.com/ubuntu bionic multiverse
# deb-src http://archive.ubuntu.com/ubuntu bionic multiverse
deb http://archive.ubuntu.com/ubuntu bionic-updates multiverse
# deb-src http://archive.ubuntu.com/ubuntu bionic-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://archive.ubuntu.com/ubuntu bionic-backports main restricted universe multiverse
# deb-src http://archive.ubuntu.com/ubuntu bionic-backports main restricted universe multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu bionic partner
# deb-src http://archive.canonical.com/ubuntu bionic partner

deb http://archive.ubuntu.com/ubuntu bionic-security main restricted
# deb-src http://archive.ubuntu.com/ubuntu bionic-security main restricted
deb http://archive.ubuntu.com/ubuntu bionic-security universe
# deb-src http://archive.ubuntu.com/ubuntu bionic-security universe
deb http://archive.ubuntu.com/ubuntu bionic-security multiverse
# deb-src http://archive.ubuntu.com/ubuntu bionic-security multiverse