pickle problem

Tracker started, with env={DMLC_TRACKER_URI=10.64.5.104, DMLC_NUM_WORKER=1, DMLC_TRACKER_PORT=9095, DMLC_NUM_SERVER=0}
train-ndcg@10: 0.86364
Traceback (most recent call last):
  File "/home/dcausse/mjolnir/venv/lib/python2.7/site-packages/mjolnir/cli/training_pipeline.py", line 173, in <module>
    main(sc, sqlContext, **args)
  File "/home/dcausse/mjolnir/venv/lib/python2.7/site-packages/mjolnir/cli/training_pipeline.py", line 90, in main
    f.write(pickle.dumps(tune_results))
  File "/usr/lib/python2.7/pickle.py", line 1374, in dumps
    Pickler(file, protocol).dump(obj)
  File "/usr/lib/python2.7/pickle.py", line 224, in dump
    self.save(obj)
  File "/usr/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/usr/lib/python2.7/pickle.py", line 663, in _batch_setitems
    save(v)
  File "/usr/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/usr/lib/python2.7/pickle.py", line 649, in save_dict
    self._batch_setitems(obj.iteritems())
  File "/usr/lib/python2.7/pickle.py", line 663, in _batch_setitems
    save(v)
  File "/usr/lib/python2.7/pickle.py", line 306, in save
    rv = reduce(self.proto)
  File "/home/dcausse/mjolnir/venv/lib/python2.7/copy_reg.py", line 84, in _reduce_ex
    dict = getstate()
  File "/home/dcausse/mjolnir/spark-2.1.0-bin-hadoop2.6/python/lib/py4j-0.10.4-src.zip/py4j/java_gateway.py", line 1133, in __call__
  File "/home/dcausse/mjolnir/spark-2.1.0-bin-hadoop2.6/python/lib/pyspark.zip/pyspark/sql/utils.py", line 63, in deco
  File "/home/dcausse/mjolnir/spark-2.1.0-bin-hadoop2.6/python/lib/py4j-0.10.4-src.zip/py4j/protocol.py", line 323, in get_return_value
py4j.protocol.Py4JError: An error occurred while calling o16634.__getstate__. Trace:
py4j.Py4JException: Method __getstate__([]) does not exist
	at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:318)
	at py4j.reflection.ReflectionEngine.getMethod(ReflectionEngine.java:326)
	at py4j.Gateway.invoke(Gateway.java:272)
	at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:132)
	at py4j.commands.CallCommand.execute(CallCommand.java:79)
	at py4j.GatewayConnection.run(GatewayConnection.java:214)
	at java.lang.Thread.run(Thread.java:745)