PySpark ML persistence failed when handle no default value parameter

This defect find when implement task spark-13033. When add below code to doctest.
It looks like _transfer_params_from_java did not consider the params which do not have default value and we should handle them.

>>> import os, tempfile
>>> path = tempfile.mkdtemp()
>>> aftsr_path = path + "/aftsr"
>>> aftsr.save(aftsr_path)
>>> aftsr2 = AFTSurvivalRegression.load(aftsr_path)

Exception detail.
ir2 = IsotonicRegression.load(ir_path)
Exception raised:
Traceback (most recent call last):
File "C:\Python27\lib\doctest.py", line 1289, in run
compileflags, 1) in test.globs
File "<doctest __main.IsotonicRegression[11]>", line 1, in
ir2 = IsotonicRegression.load(ir_path)
File "C:\aWorkFolder\spark\spark-1.6.0-bin-hadoop2.6\spark-1.6.0-bin-hadoop2.6\python\lib\pyspark.zip\pyspark\ml\util.py", line 194, in load
return cls.read().load(path)
File "C:\aWorkFolder\spark\spark-1.6.0-bin-hadoop2.6\spark-1.6.0-bin-hadoop2.6\python\lib\pyspark.zip\pyspark\ml\util.py", line 148, in load
instance.transfer_params_from_java()
File "C:\aWorkFolder\spark\spark-1.6.0-bin-hadoop2.6\spark-1.6.0-bin-hadoop2.6\python\lib\pyspark.zip\pyspark\ml\wrapper.py", line 82, in tran
fer_params_from_java
value = _java2py(sc, self._java_obj.getOrDefault(java_param))
File "C:\aWorkFolder\spark\spark-1.6.0-bin-hadoop2.6\spark-1.6.0-bin-hadoop2.6\python\lib\py4j-0.9-src.zip\py4j\java_gateway.py", line 813, in
_call
answer, self.gateway_client, self.target_id, self.name)
File "C:\aWorkFolder\spark\spark-1.6.0-bin-hadoop2.6\spark-1.6.0-bin-hadoop2.6\python\lib\pyspark.zip\pyspark\sql\utils.py", line 45, in deco
return f(a, *kw)
File "C:\aWorkFolder\spark\spark-1.6.0-bin-hadoop2.6\spark-1.6.0-bin-hadoop2.6\python\lib\py4j-0.9-src.zip\py4j\protocol.py", line 308, in get_
eturn_value
format(target_id, ".", name), value)
Py4JJavaError: An error occurred while calling o351.getOrDefault.
: java.util.NoSuchElementException: Failed to find a default value for weightCol
at org.apache.spark.ml.param.Params$$anonfun$getOrDefault$2.apply(params.scala:647)
at org.apache.spark.ml.param.Params$$anonfun$getOrDefault$2.apply(params.scala:647)
at scala.Option.getOrElse(Option.scala:120)
at org.apache.spark.ml.param.Params$class.getOrDefault(params.scala:646)
at org.apache.spark.ml.PipelineStage.getOrDefault(Pipeline.scala:43)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:483)
at py4j.reflection.MethodInvoker.invoke(MethodInvoker.java:231)
at py4j.reflection.ReflectionEngine.invoke(ReflectionEngine.java:381)
at py4j.Gateway.invoke(Gateway.java:259)
at py4j.commands.AbstractCommand.invokeMethod(AbstractCommand.java:133)
at py4j.commands.CallCommand.execute(CallCommand.java:79)
at py4j.GatewayConnection.run(GatewayConnection.java:209)
at java.lang.Thread.run(Thread.java:745)