What steps will reproduce the problem?
1. See attached beans Tree and Monkey
2. Run this test:

    Tree tree = new Tree();
    tree.getMonkeys().add(new Monkey());
    tree.getMonkeys().add(new Monkey());

    String serialised = json.toJson(tree);
    Tree newTree = json.fromJson(serialised, Tree.class);

What is the expected output? What do you see instead?

Deserialize fails, Caused by: java.lang.ClassCastException:
com.jpmorgan.ibmlbus.beans.serialise.Monkey cannot be cast to
java.lang.Comparable
    at java.util.TreeMap.put(Unknown Source)
    at java.util.TreeSet.add(Unknown Source)
    at
com.google.gson.DefaultTypeAdapters$CollectionTypeAdapter.deserialize(DefaultTyp
eAdapters.java:404)
    at
com.google.gson.DefaultTypeAdapters$CollectionTypeAdapter.deserialize(DefaultTyp
eAdapters.java:369)
    at
com.google.gson.JsonDeserializerExceptionWrapper.deserialize(JsonDeserializerExc
eptionWrapper.java:50)
    ... 27 more

The point is that Monkeys have no natural ordering. We should be able to
use them in a Set though, because uniqueness is fine.

What version of the product are you using? On what operating system?
1.2.3

Please provide any additional information below.