I'm using nokogiri to extract content from web pages and every now and
then I see this error thrown for certain pages, along with other
versions of the NoMethodError. I'm trying to understand the nature of
the error so I can be in a better position to provide fixes. The
relevant code and error message are pasted below.

nokogiri_helper.rb:

require 'nokogiri'
module NokogiriHelper

  def content_elements_for(node)
    nodes = []
    # We add node.parent because node is an
    # instance of Nokogiri::XML::Text
    # but we want the tag that contains the text.
    node.traverse{|element| nodes << element.parent if element.text? &&
element.parent.name != 'a' && has_content?(element.text)}
   ...
  end
 ...
end


ERROR (ContentExtractor)
#<NoMethodError: undefined method `traverse' for nil:NilClass>
/opt/plugins/helpers/nokogiri_helper.rb:68:in `content_elements_for'
/opt/plugins/ContentExtractor.rb:66:in `translate_one'
/opt/plugins/Translator.rb:24:in `translate'
/opt/plugins/Translator.rb:21:in `each'
/opt/plugins/Translator.rb:21:in `translate'
/opt/plugins/Translator.rb:16:in `execute'
/opt/plugins/ContentExtractor.rb:53:in `execute'
/opt/plugins/BasePlugin.rb:201:in `call'
/opt/lib/filesystem_lock_provider.rb:83:in `lock'
/opt/plugins/BasePlugin.rb:200:in `call'
/opt/lib/feed.rb:251:in `run'
/opt/lib/feed.rb:248:in `each'
/opt/lib/feed.rb:248:in `run'
/opt/lib/feed.rb:243:in `each'
/opt/lib/feed.rb:243:in `run'
/opt/lib/schedule_runner.rb:159:in `create_feed_process'
/opt/lib/schedule_runner.rb:154:in `fork'
/opt/lib/schedule_runner.rb:154:in `create_feed_process'
/opt/lib/schedule_runner.rb:325:in `run_iteration'
/opt/lib/schedule_runner.rb:269:in `run'
/opt/lib/schedule_runner.rb:268:in `loop'
/opt/lib/schedule_runner.rb:268:in `run'
bin/run_feed:57

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