public static void main(String[] args) {
		System.out.println(merge(Arrays.asList("c","c","a","a"), (a1, a2)-> {
			return a1.startsWith(a2) ? a1 + a2 : null;
		}));
		System.out.println(merge(Arrays.asList("c","c"), (a1, a2)-> {
			return a1.startsWith(a2) ? a1 + a2 : null;
		}));
		System.out.println(merge(Arrays.asList("a", "b"), (a1, a2)-> {
			return a1.startsWith(a2) ? a1 + a2 : null;
		}));
	}