Github user yanboliang commented on the issue:
https://github.com/apache/spark/pull/13353
@jkbradley I found the main problem is that the ```uid``` defined in Java
class will be initialized after Scala traits such as ```HasFeaturesCol```. So
when ```HasFeaturesCol``` being constructed, they get ```uid``` with null,
which will cause ```Param.shouldOwn``` check fail. I think moving the ```uid```
as constructor argument of ```Classifier``` will solve this problem. But it
involves public API changes such as ```Classifier```, ```Regressor```,
```ProbabilisticClassifier```, etc and should be further defined, I agree to
remove this for now.
I will track this issue and send my proposal of fix to JIRA for discussion.
I think we can find an appropriate fix it at 2.1 and adding this example back.
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