Our default serialization behavior recognizes this as a setter:

public void setAmount(double amount) {
    this.amount = amount;
}

But not this:

public Offer setAmount(double amount) {
    this.amount = amount;
    return this;
}

End result is that deserialization doesn't set the field and the user is left scratching their head and demanding justice. Look into whether we can tweak the default behavior to recognize the latter example as a setter in serialization.