@Override
        protected List<T> merge(ConfigKey key, List<List<T>> values) {
            List<T> merged = new ArrayList<>();
            for (List<T> value : values) {
                merged.addAll(value);
            }
            return merged;
        }
Data type-specific extractor to read value from properties.

@param prefix
@param key
@param properties
@return
src/main/java/io/fabric8/maven/docker/config/handler/property/ValueProvider.java