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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 get_cgi_parameter_float(form: cgi.FieldStorage, key: str) -> Optional[float]: """ Extracts a float parameter from a CGI form, or None if the key is absent or the string value is not convertible to ``float``. """

    return get_float_or_none(get_cgi_parameter_str(form, key))