@Override
  public void close() throws IOException {
    if (isEmptyInput == false)
      reader.close();
  }
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