def find_duplicate_timestamps(timestamps):
    """Find duplicate value(s) in a sequence of timestamps.

    Args:
        timestamps (list): A list of timestamps (in picoseconds).

    Returns:
        An ascendingly sorted list of duplicated timestamp values (if any).
    """
    if timestamps is None or len(timestamps) < 2:
        return None

    duplicate_timestamps = set(timestamp for timestamp in timestamps
                               if timestamps.count(timestamp) > 1)
    return sorted(duplicate_timestamps)