public final boolean readIsNull() throws TException {
    readRawAll(wasNull, 0, 1);
    lastPrimitiveWasNull = (wasNull[0] == 0);
    return lastPrimitiveWasNull;
  }
This method always return the same instance of TSet to avoid creating new
instances. It is the responsibility of the caller to read the value before
calling this method again.
serde/src/java/org/apache/hadoop/hive/serde2/thrift/TBinarySortableProtocol.java