Lesson 1 / "sudo apt update" doesn't work

In the docker container, I got the following messages and it prevents me to install other ROS2-related packages. How can I fix this?

kbu@ade:~$ sudo apt update
Ign:1 http://packages.ros.org/ros2/ubuntu bionic InRelease
Hit:2 http://archive.ubuntu.com/ubuntu bionic InRelease                                        
Err:3 http://packages.ros.org/ros2/ubuntu bionic Release                                       
  404  Not Found [IP: 10.5.1.9 80]
Hit:4 http://archive.ubuntu.com/ubuntu bionic-backports InRelease                                                        
Hit:5 http://archive.ubuntu.com/ubuntu bionic-updates InRelease                                                          
Hit:6 https://deb.nodesource.com/node_10.x bionic InRelease                                                         
Hit:7 http://security.ubuntu.com/ubuntu bionic-security InRelease                                                   
Reading package lists... Done                         
E: The repository 'http://packages.ros.org/ros2/ubuntu bionic Release' no longer has 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.