@Override
    public boolean equals(final Object o) {
        if (this == o) {
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            return false;
        }
        final MultiRefDataValueProxy that = (MultiRefDataValueProxy) o;
        return Objects.equals(refDataValueProxies, that.refDataValueProxies);
    }
Merge the two proxies into one combined one that will use each contained proxy to try to get a value.
Argument order is CRITICAL to ensure lookups are done in the correct order.

@param existingRefDataValueProxy The existing
@param newRefDataValueProxy
@return
stroom-pipeline/src/main/java/stroom/pipeline/refdata/store/MultiRefDataValueProxy.java