public void addStringOrObjPart(Object o) {
    if (o instanceof String || o == null) {
      addStringPart((String) o);
    } else {
      // Note even if o is a byte[] we need to serialize it.
      // This could be cleaned up but it would require C client code to change.
      serializeAndAddPart(o, false);
    }
  }
When building a Message this will return the number of the next Part to be added to the message
geode-core/src/main/java/org/apache/geode/internal/cache/tier/sockets/Message.java