StreamAPi Window 在使用 .evictor(TimeEvictor.of(Time.seconds(0))).sum().print 报NullPoint

[HunterXHunter]

代码如下： evictor设置的在窗口触发前清理所有数据，按理进入sum是没有数据，但是调试的时候发现，sum经过计算会输出 null 进入
print，导致报 Nullpoint。不知道是bug还是我的问题；

class A {
            String word;
            Long time;

            public A(String word, Long time) {
                this.word = word;
                this.time = time;
            }
        };
        streamEnv.fromElements(new A("a", 1L))
                .assignTimestampsAndWatermarks(
                        WatermarkStrategy.
forBoundedOutOfOrderness(Duration.ofSeconds(10))
                                .withTimestampAssigner(((element,
recordTimestamp) -> element.time))
                )
                .keyBy(x -> x.time)
        .map(x -> new Tuple2<>(x.word, 1L))
                .returns(Types.TUPLE(Types.STRING, Types.LONG))
        .keyBy((KeySelector<Tuple2&lt;String, Long>, String>) o -> o.f0)
                .window(TumblingEventTimeWindows.of(Time.seconds(20)))
                .evictor(TimeEvictor.of(Time.seconds(0)))
                .sum(1)
        .print();
        streamEnv.execute();



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