old_contents: class Link(object):
      def __init__(self, label, code, description):
          self.label = label
          self.code = code
          self.description = description
  
new_contents: class Link(object):
      def __init__(self, label=None, code=None, description=None):
          self.label = label
          self.code = code
          self.description = description
  
subject: Make all arguments to link optional