code: public static void saveSequenceFile(String path, JavaRDD<List<Writable>> rdd) {
          saveSequenceFile(path, rdd, null);
      }
docs: Save a {@code JavaRDD<List<Writable>>} to a Hadoop {@link org.apache.hadoop.io.SequenceFile}. Each record is given
  a unique (but noncontiguous) {@link LongWritable} key, and values are stored as {@link RecordWritable} instances.
  <p>
  Use {@link #restoreSequenceFile(String, JavaSparkContext)} to restore values saved with this method.
  
  @param path Path to save the sequence file
  @param rdd  RDD to save
  @see #saveSequenceFileSequences(String, JavaRDD)
  @see #saveMapFile(String, JavaRDD)