def data2str(data):
    """
    Convert some data to a string.

    An empty or None value is returned unchanged (helpful for testing), e.g.:

    '57 75 6e 64 65 72 62 61 72 49 52' -> 'WunderbarIR'
    '' -> ''
    """
    if not data: return data
    text = ''.join([chr(int(v, 16)) for v in data.split()])
    return text