code: def set_global_tracer(value):
      
      if value is None:
          raise ValueError('The global Tracer tracer cannot be None')
  
      global tracer, is_tracer_registered
      tracer = value
      is_tracer_registered = True
docs: Sets the global tracer.
      It is an error to pass ``None``.
  
      :param value: the :class:`Tracer` used as global instance.
      :type value: :class:`Tracer`