Fix case when we want a UrlConfig but the URL is nil

Previously if the `url` key in a config hash was nil we'd ignore the
configuration as invalid. This can happen when you're relying on a
`DATABASE_URL` in the env and that is not set in the environment.

```
production:
  <<: *default
  url: ENV['DATABASE_URL']
```

This PR fixes that case by checking if there is a `url` key in the
config instead of checking if the `url` is not nil in the config.

In addition to changing the conditional we then need to build a url hash
to merge with the original hash in the `UrlConfig` object.

Fixes #35091

1 files changed, 9 insertions, 4 deletions

diff --git a/activerecord/lib/active_record/database_configurations/url_config.rb b/activerecord/lib/active_record/database_configurations/url_config.rb
index 81917fc4c1..8e8aa69478 100644
--- a/activerecord/lib/active_record/database_configurations/url_config.rb
+++ b/activerecord/lib/active_record/database_configurations/url_config.rb
@@ -56,12 +56,17 @@ module ActiveRecord
       end
 
       private
-        def build_config(original_config, url)
-          if /^jdbc:/.match?(url)
-            hash = { "url" => url }
+
+        def build_url_hash(url)
+          if url.nil? || /^jdbc:/.match?(url)
+            { "url" => url }
           else
-            hash = ActiveRecord::ConnectionAdapters::ConnectionSpecification::ConnectionUrlResolver.new(url).to_hash
+            ActiveRecord::ConnectionAdapters::ConnectionSpecification::ConnectionUrlResolver.new(url).to_hash
           end
+        end
+
+        def build_config(original_config, url)
+          hash = build_url_hash(url)
 
           if original_config[env_name]
             original_config[env_name].merge(hash)