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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_tags(self, ID3=None):
 """Add an empty ID3 tag to the file. Args: ID3 (ID3):
 An ID3 subclass to use or `None` to use the one that used when loading. A custom tag reader may be used in instead of the default `ID3` object, e.g. an `mutagen.easyid3.EasyID3` reader. """


        if ID3 is None:
            ID3 = self.ID3
        if self.tags is None:
            self.ID3 = ID3
            self.tags = ID3()
        else:
            raise error("an ID3 tag already exists")