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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def add_tag(self, key, value=''):
 """ Add a tag to this object. Tag's are stored by AWS and can be used to organize and filter resources. Adding a tag involves a round-trip to the EC2 service. :type key: str :param key: The key or name of the tag being stored. :type value: str :param value: An optional value that can be stored with the tag. If you want only the tag name and no value, the value should be the empty string. """

        status = self.connection.create_tags([self.id], {key : value})
        if self.tags is None:
            self.tags = TagSet()
        self.tags[key] = value