@Override
  public byte[] getTagsArray() {
    throw new IllegalArgumentException("This is a key only Cell");
  }
A setter that helps to avoid object creation every time and whenever there is a need to create
new OffheapKeyOnlyKeyValue.
@param key    - the key part of the cell
@param offset - offset of the cell
@param length - length of the cell
@param rowLen - the rowlen part of the cell
hbase-common/src/main/java/org/apache/hadoop/hbase/ByteBufferKeyOnlyKeyValue.java