render_stream method ignoring render errors

Hi, I'm with a problem on my production enviroment.

I receive the error without any explanation: 
NoMethodError (private method `readlines' called for nil:NilClass):
  app/admin/invoice_items.rb:63:in `gen_boleto'

Looking on the code of RGhost, I found a problem on method render_stream. That ignores the possible errors ocurred on render method, and call rg.output when thats nil. It results in a nightmare error... :)

As a quick fix, I raised the errors if RGhost has errors.