@Override
  public boolean next(NullWritable nullWritable, AvroGenericRecordWritable record) throws IOException {
    if(isEmptyInput || !reader.hasNext() || reader.pastSync(stop)) {
      return false;
    }

    GenericData.Record r = (GenericData.Record)reader.next();
    record.setRecord(r);
    record.setRecordReaderID(recordReaderID);
    record.setFileSchema(reader.getSchema());

    return true;
  }
Attempt to retrieve the reader schema.  We have a couple opportunities
to provide this, depending on whether or not we're just selecting data
or running with a MR job.
@return  Reader schema for the Avro object, or null if it has not been provided.
@throws AvroSerdeException
ql/src/java/org/apache/hadoop/hive/ql/io/avro/AvroGenericRecordReader.java