title: Spark Structured Streaming: path not specified error
body: <p>Trying to write data to Kafka topic using Spark Structured Streaming and getting following error.</p>
  
  <pre class="lang-java prettyprint-override"><code>aggregatedDataset
          .select(to_json(struct("*")).as("value"))
          .writeStream()
          .outputMode(OutputMode.Append())
          .option("kafka.bootstrap.servers", kafkaBootstrapServersString)
          .option("topic", topic)
          .option("checkpointLocation", checkpointLocation)
          .start();
  </code></pre>
  
  <p>Stacktrace:</p>
  
  <pre><code>Exception in thread "main" java.lang.IllegalArgumentException: 'path' is not specified
      at org.apache.spark.sql.execution.datasources.DataSource$$anonfun$11.apply(DataSource.scala:276)
      at org.apache.spark.sql.execution.datasources.DataSource$$anonfun$11.apply(DataSource.scala:276)
      at scala.collection.MapLike$class.getOrElse(MapLike.scala:128)
      at org.apache.spark.sql.catalyst.util.CaseInsensitiveMap.getOrElse(CaseInsensitiveMap.scala:28)
      at org.apache.spark.sql.execution.datasources.DataSource.createSink(DataSource.scala:275)
      at org.apache.spark.sql.streaming.DataStreamWriter.start(DataStreamWriter.scala:286)
  </code></pre>