from_json with None crashes event stream

[nisbus]

When listening to the event stream for some reason some event is None.
When that happens, from_json crashes the stream subscription.

File "/lib/python3.7/site-packages/marathon/client.py", line 795, in event_stream
    yield ef.process(event_data)
  File "/lib/python3.7/site-packages/marathon/models/events.py", line 215, in process
    return clazz.from_json(event)
  File "/lib/python3.7/site-packages/marathon/models/base.py", line 43, in from_json
    return cls(**{to_snake_case(k): v for k, v in attributes.items()})
  File "/lib/python3.7/site-packages/marathon/models/events.py", line 36, in __init__
    self._set(attribute, kwargs.get(attribute))
  File "/lib/python3.7/site-packages/marathon/models/events.py", line 56, in _set
    attribute = self.__to_marathon_object(attribute_name, attribute)
  File "/lib/python3.7/site-packages/marathon/models/events.py", line 42, in __to_marathon_object
    attribute = clazz.from_json(attribute)
  File "/lib/python3.7/site-packages/marathon/models/base.py", line 43, in from_json
    return cls(**{to_snake_case(k): v for k, v in attributes.items()})
  File "/lib/python3.7/site-packages/marathon/models/deployment.py", line 74, in __init__
    self.original = MarathonDeploymentOriginalState.from_json(original)
  File "/lib/python3.7/site-packages/marathon/models/base.py", line 43, in from_json
    return cls(**{to_snake_case(k): v for k, v in attributes.items()})
AttributeError: 'NoneType' object has no attribute 'items'