Ubuntu 18.04: Error resolving "hotspot_name": Name or service not known

I installed Ubuntu 18.04. Yesterday I had no trouble with WiFi connection. Today, I connect to the same hotspot but I am not able to connect:

Error resolving 'hotspot_name': Name or service not known

Here is how I set the content of the relevant files:

/etc/hostname

begueradj

/etc/hosts

17.0.0.1 localhost
17.0.1.1 begueradj

I did not have /etc/cloud/cloud.cfg but I created it and set: preserve_hostname: true

I run: sudo service network-manager restart

I am still getting the same problem

Any suggestions?