backup

# File lib/bundler/environment_preserver.rb, line 30
    def backup
      env = @original.clone
      @keys.each do |key|
        value = env[key]
        if !value.nil? && !value.empty?
          env[@prefix + key] ||= value
        elsif value.nil?
          env[@prefix + key] ||= INTENTIONALLY_NIL
        end
      end
      env
    end