README.md in fluent-mixin-plaintextformatter-0.2.4 vs README.md in fluent-mixin-plaintextformatter-0.2.5

@@ -59,10 +59,11 @@
       config_set_default :field_separator, 'TAB'
       config_set_default :add_newline, true
       config_set_default :time_format, nil   # nil means ISO8601 '2012-07-13T19:29:49+09:00'
       config_set_default :remove_prefix, nil
       config_set_default :default_tag, nil
+      config_set_default :null_value, 'NULL'
       
       # ...
     end
 
 Provided configurations are below:
@@ -78,16 +79,19 @@
 * time_format
   * format string like '%Y-%m-%d %H:%M:%S' or you want
 * remove_prefix
   * input tag 'test.foo' with 'remove_prefix test', output tag is 'foo'.
   * 'default\_tag' configuration is used when input tag is completely equal to 'remove\_prefix'
+* null_value
+  * output value if value is null(nil). default is 'NULL'.
 
 ## AUTHOR / CONTRIBUTORS
 
 * AUTHOR
   * TAGOMORI Satoshi <[e-mail]>
 * CONTRIBUTORS
   * wolfg1969 https://github.com/wolfg1969
+  * Shinya Okano <[e-mail]>
 
 ## LICENSE
 
 * Copyright: Copyright (c) 2012- tagomoris
 * License: Apache License, Version 2.0