One field in Protocol Buffers is always missing when reading from SequenceFile

Question

Something mysterious is happening for me:

What I wanted to do:

1. Save a Protocol Buffers object as SequenceFile format.
2. Read this SequenceFile text and extract the field that I need.

The mystery part is: One field that I wanted to retrieve is always null.

Product_Perf is the field that I wanted to extract from SequencFiles that is always missing.

Here's my protocol buffers schema:

message ProductJoin {
Signals signals = 1;
int64 id = 2;
}

message Signals {
ProductPerf product_perf = 1;
}

message ProductPerf {
    int64 impressions = 1;
}

Here's how I save the protocol buffers as SequenceFiles:

JavaPairRDD<BytesWritable, BytesWritable> bytesWritableJavaPairRdd =
                flattenedPjPairRdd.mapToPair(
                    new PairFunction<Tuple2<Long, ProductJoin>, BytesWritable, BytesWritable>() {

                        @Override
                        public Tuple2<BytesWritable, BytesWritable> call(Tuple2<Long, ProductJoin> longProductJoinTuple2) throws Exception {
                                return new Tuple2<>(
new BytesWritable(longProductJoinTuple2._2().getId().getBytes()),
new BytesWritable(longProductJoinTuple2._2().toByteArray()));
                            }
                        }
    //dump SequenceFiles
                bytesWritableJavaPairRdd.saveAsHadoopFile(
                    "/tmp/path/",
                    BytesWritable.class,
                    BytesWritable.class,
                    SequenceFileOutputFormat.class
                );

Below is the code that how I read the SequenceFile:

 sparkSession.sparkContext()
            .sequenceFile("tmp/path", BytesWritable.class, BytesWritable.class)
            .toJavaRDD()
            .mapToPair(
                bytesWritableBytesWritableTuple2 -> {
                    Method parserMethod = clazz.getDeclaredMethod("parser");
                    Parser<T> parser = (Parser<T>) parserMethod.invoke(null);
                    return new Tuple2<>(
                        Text.decode(bytesWritableBytesWritableTuple2._1().getBytes()),
                        parser.parseFrom(bytesWritableBytesWritableTuple2._2().getBytes()));
                }
            );