getting title was failed (RuntimeError) (plugin/ref_tools.rb):91:in `get_title' ./tdiary.rb:110:in `join' ./tdiary.rb:110:in `safe' ./tdiary.rb:801:in `eval_src' ./tdiary.rb:1152:in `do_eval_rhtml' ./tdiary.rb:1089:in `eval_rhtml' ./tdiary.rb:1780:in `eval_rhtml' index.rb:81