@Override
    public void write(MapJoinObjectSerDeContext valueContext, ObjectOutputStream out) {
      throw new RuntimeException(this.getClass().getCanonicalName() + " cannot be serialized");
    }
Sometimes, when container is empty in multi-table mapjoin, we need to add a dummy row.
This container does not normally support adding rows; this is for the dummy row.
ql/src/java/org/apache/hadoop/hive/ql/exec/persistence/MapJoinBytesTableContainer.java