Error regenerating docker file

```
.gem/ruby/3.3.5/gems/dockerfile-rails-1.7.3/lib/generators/dockerfile_generator.rb:1618:in `+': no implicit conversion of nil into String (TypeError)

subsection + spaces + %(url: <%= URI.parse(ENV["DATABASE_URL"]).tap { |url| url.path += "_#{name}" } if ENV["DATABASE_URL"] %>\n)

from /Users/prometheus/.gem/ruby/3.3.5/gems/dockerfile-rails-1.7.3/lib/generators/dockerfile_generator.rb:1618:in `block in fix_database_config'
from /Users/prometheus/.gem/ruby/3.3.5/gems/dockerfile-rails-1.7.3/lib/generators/dockerfile_generator.rb:1609:in `gsub'
from /Users/prometheus/.gem/ruby/3.3.5/gems/dockerfile-rails-1.7.3/lib/generators/dockerfile_generator.rb:1609:in `fix_database_config'
from /Users/prometheus/.gem/ruby/3.3.5/gems/dockerfile-rails-1.7.3/lib/generators/dockerfile_generator.rb:341:in `generate_app'
```

I'm on rails 8 and this is my db config for prod

```
production:
# we use DATABASE_URL secret stored in Fly.io
primary:
<<: *default
database: my_db
cache:
adapter: sqlite3
database: storage/production_cache.sqlite3
migrations_paths: db/cache_migrate
queue:
adapter: sqlite3
database: storage/production_queue.sqlite3
migrations_paths: db/queue_migrate
cable:
adapter: sqlite3
database: storage/production_cable.sqlite3
migrations_paths: db/cable_migrate
```