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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 join_css_class(css_class, *additional_css_classes):
 """ Returns the union of one or more CSS classes as a space-separated string. Note that the order will not be preserved. """

    css_set = set(chain.from_iterable(
        c.split(' ') for c in [css_class, *additional_css_classes] if c))
    return ' '.join(css_set)