@Override
  public KnownVersion[] getSerializationVersions() {
    return null;
  }
Same as {@link #replace(Object, Object)} except a callback argument is supplied to be passed on
to <tt>CacheListener</tt>s and/or <tt>CacheWriter</tt>s.
<p>
TODO: callbackArg is always null but this method is for callbacks??
geode-core/src/main/java/org/apache/geode/internal/cache/LocalRegion.java