fluent/fluentd · error · ConfigError

'#{key}' doesn't have default value

Error message

'#{key}' doesn't have default value

What it means

Error "'#{key}' doesn't have default value" thrown in fluent/fluentd.

Source

Thrown at lib/fluent/config/section.rb:141

          section_stack = ", in section " + stack.join(" > ")
        end

        section_params = {}

        proxy.defaults.each_pair do |name, defval|
          varname = name.to_sym
          section_params[varname] = (defval.dup rescue defval)
        end

        if proxy.argument
          unless conf.arg.nil? || conf.arg.empty?
            key, block, opts = proxy.argument
            opts = opts.merge(strict: true) if strict_config_value

            if conf.arg == :default
              unless section_params.has_key?(key)
                logger.error "config error in:\n#{conf}" if logger
                raise ConfigError, "'#{key}' doesn't have default value"
              end
            else
              begin
                section_params[key] = self.instance_exec(conf.arg, opts, key, &block)
              rescue ConfigError => e
                logger.error "config error in:\n#{conf}" if logger
                raise e
              end
            end
          end
          unless section_params.has_key?(proxy.argument.first)
            logger.error "config error in:\n#{conf}" if logger # logger should exist, but sometimes it's nil (e.g, in tests)
            raise ConfigError, "'<#{proxy.name} ARG>' section requires argument" + section_stack
          end
          # argument should NOT be deprecated... (argument always has a value: '')
        end

        proxy.params.each_pair do |name, defval|

View on GitHub (pinned to dd45c6e18d)

When it happens

Trigger: Thrown at lib/fluent/config/section.rb:141 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of fluent/fluentd@dd45c6e18d (2026-08-21). Data as JSON: /api/errors/5a027cc1af575fc7. Report an issue: GitHub.