'If the key is not found try to determine a status from Quality
:param key: A numeric key or None
:raise KeyError: if the key is invalid and can\'t be determined from Quality'

def __missing__(self, key):

    key = self.numeric(key)
    if (key in self.qualities):
        (status, quality) = Quality.splitCompositeStatus(key)
        return (self[status] if (not quality) else (((self[status] + u'    (') + Quality.qualityStrings[quality]) + u')'))
    else:
        raise KeyError(key)
