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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):
 """Add a Vorbis comment block to the file."""

        if self.tags is None:
            self.tags = VCFLACDict()
            self.metadata_blocks.append(self.tags)
        else:
            raise FLACVorbisError("a Vorbis comment already exists")