找出解决方案：

文档中存在提示： https://github.com/datastax/spark-cassandra- 设置数据集的连接器特定选项
主题下的connector / blob / master / doc / 14_data_frames.md 。

A hint is present in the document: https://github.com/datastax/spark-cassandra-connector/blob/master/doc/14_data_frames.md under Setting Connector Specific Options on Datasets topic.

确切的代码如下：

transformedData.write.format("org.apache.spark.sql.cassandra").option("header","false").option("spark.cassandra.output.ignoreNulls", true).mode("append").options(Map( "table" -> table_name, "keyspace" -> keyspace_name)).save()