diff --git a/app/models/concerns/fluentd/setting/plugin_parameter.rb b/app/models/concerns/fluentd/setting/plugin_parameter.rb
index 5dc701f..355b6ea 100644
--- a/app/models/concerns/fluentd/setting/plugin_parameter.rb
+++ b/app/models/concerns/fluentd/setting/plugin_parameter.rb
@@ -79,6 +79,7 @@ class Fluentd
 
       def reformat_value(name, value)
         type = column_type(name)
+        return value if type.nil? # name == :time_key
         return value if type == :enum
         return value if type == :regexp
         type_name = if type.is_a?(Fluentd::Setting::Type::Time)