Fix "not initialized" warnings

[algodave]

I'm proposing this PR in order to avoid instance variable not initialized warnings

[ronwsmith]

Thanks for the contrib! When do you see these errors occurring?

[ronwsmith]

Let's do || here.

[algodave]

@ronwsmith said

Thanks for the contrib! When do you see these errors occurring?

I'm using puffing-billy configured this way:

# in spec/support/billy.rb
Billy.configure do |c|
  c.cache = true
  c.persist_cache = true
end
Billy.config.logger.level = Logger::ERROR
Capybara.default_driver = :poltergeist_billy

# in my rspec contexts
      before do
        Billy.configure do |c|
          c.cache_path = 'spec/billy/my_context_path'
          c.merge_cached_responses_whitelist = [
            /useless-domain-one\.com/,
            /useless-domain-two\.com/
          ]
        end
      end