@Override
  public void writeExternal(ObjectOutput out) throws IOException {
    toData(out, InternalDataSerializer.createSerializationContext(out));
  }
Abstract class for subclasses that want to be Externalizable in addition to being
DataSerializableFixedID.
<p>
Note: subclasses must also provide a zero-arg constructor

@since GemFire 5.7
geode-core/src/main/java/org/apache/geode/internal/ExternalizableDSFID.java