def set_global_tracer(value):
    """Sets the global tracer.
    It is an error to pass ``None``.

    :param value: the :class:`Tracer` used as global instance.
    :type value: :class:`Tracer`
    """
    if value is None:
        raise ValueError('The global Tracer tracer cannot be None')

    global tracer, is_tracer_registered
    tracer = value
    is_tracer_registered = True