PostgreSQL: pg driver expects nil instead of empty string for missing user/pass

activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb

@@ -23,8 +23,8 @@ def self.postgresql_connection(config) # :nodoc:
       config = config.symbolize_keys
       host     = config[:host]
       port     = config[:port] || 5432
-      username = config[:username].to_s
-      password = config[:password].to_s
+      username = config[:username].to_s if config[:username]
+      password = config[:password].to_s if config[:password]
 
       if config.has_key?(:database)
         database = config[:database]