def who_create(user_id, ticket = None):
    """
    Create a TTBD user descriptor from a user id name and a ticket

    :params str user_id: user's name / ID
    :params str ticket: (optional) ticket for the reservation

    :returns: (str) user id descriptor
    """
    if ticket != None and ticket != "":
        return user_id + ":" + ticket
    else:
        return user_id