create pyspark livy session returns "Can not create a Path from an empty string"

Using curl to create to pyspark livy session just like http://gethue.com/how-to-use-the-livy-spark-rest-job-server-for-interactive-spark-2-2/ to me to:

curl -X POST --data '

{"kind": "pyspark"}

' -H "Content-Type: application/json" localhost:8998/sessions

it returns :
"Can not create a Path from an empty string"

just this response ,nothing else. no error message in livy log.

the livy jar file which LivyServer process dependended on is :

rw-rr-. 1 appuser appuser 8.9K Dec 27 10:10 livy-api-0.3.0-SNAPSHOT.jar
rw-rr-. 1 appuser appuser 19K Dec 27 10:10 livy-client-common-0.3.0-SNAPSHOT.jar
rw-rr-. 1 appuser appuser 87K Dec 27 10:10 livy-core_2.11-0.3.0-SNAPSHOT.jar
rw-rr-. 1 appuser appuser 119K Dec 27 10:10 livy-rsc-0.3.0-SNAPSHOT.jar
rw-rr-. 1 appuser appuser 570K Dec 27 10:10 livy-server-0.3.0-SNAPSHOT.jar

So , it seems that it is a 0.3.0 livy server.

and the spark version is :
spark-2.0.0-bin-hadoop2.7

my hdfs is ok.

When I run pyspark directly ,everything is ok.

The response message is so generic and the only thing I know is that the spark trying to new a Path() object but the path parameter is null or an empty "".

But I cannot get any error stacktrace.

Anyone can help me?