import time


def parse_timestamp(t):
    """Parses a string containing a timestamp.

    Args:
        t (str): A string containing a timestamp.

    Returns:
        time.struct_time: A timestamp.
    """
    if t is None or t == '0000-00-00T00:00:00Z':
        return time.struct_time((0, 0, 0, 0, 0, 0, 0, 0, 0))
    return time.strptime(t, '%Y-%m-%dT%H:%M:%SZ')