public void set(int index, BytesRefWritable bytesRefWritable) {
    ensureCapacity(index + 1);
    bytesRefWritables[index] = bytesRefWritable;
    if (valid <= index) {
      valid = index + 1;
    }
  }
Set the BytesRefWritable at the specified position with the specified
BytesRefWritable.

@param index
         index position
@param bytesRefWritable
         the new element
@throws IllegalArgumentException
          if the specified new element is null
serde/src/java/org/apache/hadoop/hive/serde2/columnar/BytesRefArrayWritable.java