A utility of collection functions. 1. Denormalize a java Map<K,List<T>> into a list of entries 2. firstOrNull in a list

CollectionUtils.java

private <K,T> List<Map.Entry<K, T>> denormalizeMap(Map<K,List<T>> nestedListMap) {
        List<Map.Entry<K, T>> denormalizedEntryList = new ArrayList<Map.Entry<K,T>>();
        for(Map.Entry<K, List<T>> entry:nestedListMap.entrySet()) {
            for(T t:entry.getValue()) {
                denormalizedEntryList.add(new AbstractMap.SimpleEntry<K,T>(entry.getKey(), t));
            }
        }
        return denormalizedEntryList;
    }

public static <T> T firstOrNull(List<T> list) {
        if(list == null || list.isEmpty()) {
            return null;
        } else {
            return list.get(0);
        }
    }

AbstractMap.SimpleEntry is public starting from Java 1.6, so this only works with that.