Installazione della CLI del tema e creazione di un tema

Non volevo ingombrare quell’argomento, ma stavo seguendo questa guida

quando sono arrivato a questo passaggio

invece ho ottenuto

/var/lib/gems/3.0.0/gems/discourse_theme-2.1.6/lib/discourse_theme/scaffold.rb:53:in `block in generate': undefined method `safe_dump' for Psych:Module (NoMethodError)
Did you mean?  safe_load
	from /var/lib/gems/3.0.0/gems/discourse_theme-2.1.6/lib/discourse_theme/scaffold.rb:18:in `chdir'
	from /var/lib/gems/3.0.0/gems/discourse_theme-2.1.6/lib/discourse_theme/scaffold.rb:18:in `generate'
	from /var/lib/gems/3.0.0/gems/discourse_theme-2.1.6/lib/discourse_theme/cli.rb:68:in `run'
	from /var/lib/gems/3.0.0/gems/discourse_theme-2.1.6/bin/discourse_theme:6:in `\u003ctop (required)\u003e'
	from /usr/local/bin/discourse_theme:25:in `load'
	from /usr/local/bin/discourse_theme:25:in `\u003cmain\u003e'

ho fatto qualcosa di sbagliato?