"fluent-plugin-config-format" can't handle some plugins in the markdown format

[nokute78]

Check CONTRIBUTING guideline first and here is the list to help us investigate the problem.

• fluentd or td-agent version.
  fluentd 0.14.16

• Environment information, e.g. OS.
  CentOS 6.9
  ruby 2.3.0p0 (2015-12-25 revision 53290) [x86_64-linux]

• Your configuration
  none.
  The issue is about "fluent-plugin-config-format"

• Your problem explanation. If you have an error logs, write it together.

"fluent-plugin-config-format" doesn't work for some plugins. (e.g. out_null)
The issue is only happened when the format is markdown.

$ bundle exec bin/fluent-plugin-config-format output null
bundler: failed to load command: bin/fluent-plugin-config-format (bin/fluent-plugin-config-format)
NoMethodError: undefined method `trace' for nil:NilClass
Did you mean?  trace_var
               trap
  /home/taka/git/oss/fluentd/lib/fluent/command/plugin_config_formatter.rb:170:in `block in dump_section_markdown'
  /home/taka/git/oss/fluentd/lib/fluent/command/plugin_config_formatter.rb:166:in `each'
  /home/taka/git/oss/fluentd/lib/fluent/command/plugin_config_formatter.rb:166:in `dump_section_markdown'
  /home/taka/git/oss/fluentd/lib/fluent/command/plugin_config_formatter.rb:144:in `block in dump_markdown'
  /home/taka/git/oss/fluentd/lib/fluent/command/plugin_config_formatter.rb:141:in `each'
  /home/taka/git/oss/fluentd/lib/fluent/command/plugin_config_formatter.rb:141:in `dump_markdown'
  /home/taka/git/oss/fluentd/lib/fluent/command/plugin_config_formatter.rb:67:in `call'
  bin/fluent-plugin-config-format:5:in `<top (required)>'

'$log' seems not to be initialized.
The workaround is to comment out like this and the tool will work correctly.

$ git diff
diff --git a/lib/fluent/command/plugin_config_formatter.rb b/lib/fluent/command/plugin_config_formatter.rb
index c1b6621..e77bf85 100644
--- a/lib/fluent/command/plugin_config_formatter.rb
+++ b/lib/fluent/command/plugin_config_formatter.rb
@@ -167,7 +167,7 @@ class FluentPluginConfigFormatter
       required = sub_section.delete(:required)
       multi = sub_section.delete(:multi)
       alias_name = sub_section.delete(:alias)
-      $log.trace(name: section_name, required: required, multi: multi, alias_name: alias_name)
+#      $log.trace(name: section_name, required: required, multi: multi, alias_name: alias_name)
       sub_section.delete(:section)
       dumped << ERB.new(template_path("section.md.erb").read, nil, "-").result(binding)
     end

[repeatedly]

Thanks for the report!
#1585 fixes it.

[nokute78]

Thanks!