remove leading/trailing whitespace and always return unicode.

def sanitize_string(string_or_unicode):
    """
    remove leading/trailing whitespace and always return unicode.
    """
    if isinstance(string_or_unicode, unicode):
        return string_or_unicode.strip()
    elif isinstance(string_or_unicode, str):
        return string_or_unicode.decode('utf-8').strip()
    else:  # e.g. if input is None
        return u''