def split_registrations(list_of_registrations):
    """Groups registrations at the same service together.

    This function generates a nested list of registrations. Registrations
    in the same sublist are registered at the same conductor service.

    :param list list_of_registrations: list of dict objects
    :return: nested list of registrations
    """
    list_of_registrations.sort(key=lambda registration: registration.service)

    sub_list = []
    main_list = []
    previous = list_of_registrations[0]

    for registration in list_of_registrations:
        if previous.service == registration.service:
            sub_list.append(registration)
        else:
            main_list.append(sub_list)
            sub_list = [registration]
        previous = registration

    main_list.append(sub_list)
    return main_list