fix: 'SparkSession' object has no attribute 'util' (#557)

Signed-off-by: Jason Wang <jasowang@microsoft.com>

onnxmltools/convert/sparkml/operator_converters/tree_ensemble_common.py

@@ -4,7 +4,7 @@
 import os
 import time
 import numpy
-
+from pyspark.sql import SparkSession
 
 class SparkMLTree(dict):
     pass
@@ -31,10 +31,11 @@ def sparkml_tree_dataset_to_sklearn(tree_df, is_classifier):
     return tree
 
 
-def save_read_sparkml_model_data(spark, model):
+def save_read_sparkml_model_data(spark: SparkSession, model):
     tdir = tempfile.tempdir
     if tdir is None:
-        tdir = spark.util.Utils.createTempDir().getAbsolutePath()
+        local_dir = spark._jvm.org.apache.spark.util.Utils.getLocalDir(spark._jsc.sc().conf())
+        tdir = spark._jvm.org.apache.spark.util.Utils.createTempDir(local_dir, "onnx").getAbsolutePath()
     if tdir is None:
         raise FileNotFoundError(
             "Unable to create a temporary directory for model '{}'"