public void append(final Object o) {
        if (o == null) {
            hashCode = hashCode * 31;
        } else {
            hashCode = hashCode * 31 + o.hashCode();
        }
    }
A GWT friendly version of commons HashCodeBuilder.
stroom-legacy/stroom-legacy-model_6_1/src/main/java/stroom/legacy/model_6_1/HashCodeBuilder.java