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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 normalize_extension(extension):
 """Normalise a file name extension."""

    extension = decode_path(extension)
    if extension is None:
        return
    if extension.startswith('.'):
        extension = extension[1:]
    if '.' in extension:
        _, extension = os.path.splitext(extension)
    extension = slugify(extension, sep='')
    if extension is None:
        return
    if len(extension):
        return extension