/usr/lib/ruby/vendor_ruby/active_record/connection_adapters/nulldb_adapter/ is in ruby-activerecord-nulldb-adapter 0.3.2-1.
This file is owned by root:root, with mode 0o755.
..
/usr/lib/ruby/vendor_ruby/active_record/connection_adapters/nulldb_adapter/checkpoint.rb
/usr/lib/ruby/vendor_ruby/active_record/connection_adapters/nulldb_adapter/column.rb
/usr/lib/ruby/vendor_ruby/active_record/connection_adapters/nulldb_adapter/configuration.rb
/usr/lib/ruby/vendor_ruby/active_record/connection_adapters/nulldb_adapter/core.rb
/usr/lib/ruby/vendor_ruby/active_record/connection_adapters/nulldb_adapter/empty_result.rb
/usr/lib/ruby/vendor_ruby/active_record/connection_adapters/nulldb_adapter/index_definition.rb
/usr/lib/ruby/vendor_ruby/active_record/connection_adapters/nulldb_adapter/null_object.rb
/usr/lib/ruby/vendor_ruby/active_record/connection_adapters/nulldb_adapter/statement.rb
/usr/lib/ruby/vendor_ruby/active_record/connection_adapters/nulldb_adapter/table_definition.rb