AttributeError：“ NoneType”对象在indexedRowMatrix columnSimilarities（）

Question

我正在处理之前已正确使用数据框执行的代码，但是这一次执行时，出现错误。 （唯一的区别是这次我在数据帧上使用了persist()。）

simMat = IndexedRMat.columnSimilarities()

正确执行，然后执行此部分：

columns = ['product1', 'product2', 'sim']
vals = simMat.entries.map(lambda e: (e.i, e.j, e.value)).collect()
dfsim = spark.createDataFrame(vals, columns)  

产生此错误：

 AttributeErrorTraceback (most recent call last)
    <ipython-input-100-11502084c71b> in <module>()
          1 columns = ['product1', 'product2', 'sim']
    ----> 2 vals = simMat.entries.map(lambda e: (e.i, e.j, e.value)).collect()
          3 dfsim = spark.createDataFrame(vals, columns)

    /opt/spark-2.3.0-SNAPSHOT-bin-spark-master/python/pyspark/rdd.pyc in collect(self)
        806             to be small, as all the data is loaded into the driver's memory.
        807         """
    --> 808         with SCCallSiteSync(self.context) as css:
        809             port = self.ctx._jvm.PythonRDD.collectAndServe(self._jrdd.rdd())
        810         return list(_load_from_socket(port, self._jrdd_deserializer))

    /opt/spark-2.3.0-SNAPSHOT-bin-spark-master/python/pyspark/traceback_utils.pyc in __enter__(self)
         70     def __enter__(self):
         71         if SCCallSiteSync._spark_stack_depth == 0:
    ---> 72             self._context._jsc.setCallSite(self._call_site)
         73         SCCallSiteSync._spark_stack_depth += 1
         74 

    AttributeError: 'NoneType' object has no attribute 'setCallSite'

是什么意思？我是新来的人，却找不到这种错误的解释。