title: How can I work with this Module/Class setup?
body: <p>I have the following module/class:</p>
  
  <pre><code>module Pigeons
    class FedEx
  
      attr_accessor :signature_name
  
      def initialize(account)
        self.account = account
      end
  
      def response(number)
        body = "...some xml..."
        return HTTParty.post('http://example.com', :body =&gt; body)
      end
  
      def track(number)
        details = response(number)
  
        self.signature_name = details[:delivery_signature_name]      
      end 
    end
  end
  </code></pre>
  
  <p>What I'd like to be able to do is this: </p>
  
  <pre><code>@fedex ||= Pigeons::FedEx.new('123abc')
  tracker = fedex.track('1234567890')
  tracker.signature_name
  </code></pre>
  
  <p>Everything is working up until the <code>tracker.signature_name</code> part, which throws an <code>undefined method 'signature_name' for nil:NilClass</code> error.</p>