@Override
        public Key read(final DataReader reader) {
            // Read single key part.
            final GroupKeyPart groupKeyPart = new GroupKeyPart(ValSerialiser.readArray(reader));
            final List<KeyPart> list = Collections.singletonList(groupKeyPart);
            return new Key(0, list);
        }
Creates a flat group key. <GROUP VAL ARRAY>
stroom-query/stroom-query-common/src/main/java/stroom/query/common/v2/KeyFactoryFactory.java