我正试图用paypal_adaptive gem开发一个小型应用程序，但每次我都尝试这样做：
ipn=PaypalAdaptive:：IpNotification.new
它可以进行开发，但在使用mysql的生产中失败，并出现以下错误：
NoMethodError:未定义的方法to_sym' for nil:NilClass
from /usr/local/rvm/gems/ruby-1.9.3-p327/gems/paypal_adaptive-0.3.2/lib/paypal_adaptive/config.rb:28:ininitialize'来自/usr/local/rvm/gems/ruby-1.9.3-p327/gems/paypala_adapive-0.3.2/lib/paypal_adapive/config.rb:69:innew'
from /usr/local/rvm/gems/ruby-1.9.3-p327/gems/paypal_adaptive-0.3.2/lib/paypal_adaptive/config.rb:69:inconfig'来自/usr/local/rvm/gems/ruby-1.9.3-p327/gems/paypala_adaptive-0.3.2/lib/paypal_adaptive/ipn_notification.rb:9:在initialize'
from (irb):1:in新'来自(irb)：1从/usr/local/rvm/gems/ruby-1.9.3-p327/gems/railties-3.28/lib/rails/commands/console.rb:47:instart'
from /usr/local/rvm/gems/ruby-1.9.3-p327/gems/railties-3.2.8/lib/rails/commands/console.rb:8:instart'来自/usr/local/rvm/gems/ruby-1.9.3-p327/gems/railties-3.28/lib/rails/commands.rb:41:in<top (required)>'
from script/rails:6:inrequire'从脚本/轨道：6:在"中
没关系。我发现配置文件中少了一行。这是一个愚蠢的错误，我在考试中没有看到。