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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 sanitize_release_group(string):
 """Sanitize a `release_group` string to remove content in square brackets. :param str string: the release group to sanitize. :return: the sanitized release group. :rtype: str """

    # only deal with strings
    if string is None:
        return

    # remove content in square brackets
    string = re.sub(r'\[\w+\]', '', string)

    # strip and upper case
    return string.strip().upper()