Plugin Error

Errors in plugins? Retry to Update or Configure.

TypeError
no implicit conversion of nil into String
/home/yatabe/www/tdiary-v5.1.0/lib/aws/sig_v4.rb:35:in `+'
/home/yatabe/www/tdiary-v5.1.0/lib/aws/sig_v4.rb:35:in `signature'
/home/yatabe/www/tdiary-v5.1.0/lib/aws/pa_api.rb:46:in `get_items'
(plugin/amazon.rb):158:in `rescue in amazon_get'
(plugin/amazon.rb):151:in `amazon_get'
(plugin/amazon.rb):274:in `isbn_image_left'
(TDiary::Plugin#eval_src):49:in `eval_src'
/home/yatabe/www/tdiary-v5.1.0/lib/tdiary/plugin.rb:95:in `eval'
/home/yatabe/www/tdiary-v5.1.0/lib/tdiary/plugin.rb:95:in `eval_src'
/home/yatabe/www/tdiary-v5.1.0/lib/tdiary/base.rb:65:in `do_eval_rhtml'
/home/yatabe/www/tdiary-v5.1.0/lib/tdiary/base.rb:29:in `eval_rhtml'
/home/yatabe/www/tdiary-v5.1.0/lib/tdiary/view.rb:140:in `eval_rhtml'
/home/yatabe/www/tdiary-v5.1.0/lib/tdiary/dispatcher/index_main.rb:37:in `run'
/home/yatabe/www/tdiary-v5.1.0/lib/tdiary/dispatcher/index_main.rb:5:in `run'
/home/yatabe/www/tdiary-v5.1.0/lib/tdiary/dispatcher.rb:25:in `dispatch_cgi'
index.rb:32:in `<main>'