Java8新特性相关

1.使用流分组，遇到null会报错。
public static void main(String[] args) {

    Map<String,String> map = new HashMap<>();
    map.put("name","123");


    Map<String,String> map2 = new HashMap<>();
    map.put("name","345");

    Map<String,String> map3 = new HashMap<>();
    map.put("name",null);

    List<Map> list = new ArrayList<>();
    list.add(map);
    list.add(map3);list.add(map2);


    list.stream().collect(Collectors.groupingBy(r -> r.get("name")));
}

抛出异常：
Exception in thread "main" java.lang.NullPointerException: element cannot be mapped to a null key
at java.util.Objects.requireNonNull(Objects.java:228)
at java.util.stream.Collectors.lambda$groupingBy$159(Collectors.java:907)
at java.util.stream.ReduceOps$3ReducingSink.accept(ReduceOps.java:169)
at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1374)
at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:481)
at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:471)
at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)
at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:499)
at StringTest.main(StringTest.java:33)