@Override
    public ErrorMessage clone() {
        try {
            return (ErrorMessage) super.clone();
        } catch (CloneNotSupportedException e) {
            throw new RuntimeException("Programming error");
        }
    }
Two error messages are equal if they have the same code and message.
The cause is ignored in the comparison.
container-core/src/main/java/com/yahoo/processing/request/ErrorMessage.java