Tumbling window apply will not "fire"

[John Smith]

Hi I have the following job... I'm expecting the System.out
.println(key.toString());   to at least print, but nothing prints.

- .flatMap: Fires prints my debug message once as expected.
- .keyBy: Also fires, but prints my debug message twice.
- .apply: Doesn't seem to fire. The debug statement doesn't seem to print.
I'm expecting it to print the key from above keyBy.

DataStream<MyEvent> slStream = env.fromSource(kafkaSource,
WatermarkStrategy.noWatermarks(), "Kafka Source")
        .uid(kafkaTopic).name(kafkaTopic)
        .setParallelism(1)
        .flatMap(new MapToMyEvent("my-event", "message")) // <--- This works
        .uid("map-json-logs").name("map-json-logs");
        slStream.keyBy(new MinutesKeySelector(windowSizeMins)) // <---
This prints twice
        .window(TumblingEventTimeWindows.of(Time.minutes(windowSizeMins)))
                .apply(new WindowFunction<MyEvent, MyEvent,
Tuple3<String, String, String>, TimeWindow>() {
            @Override
            public void apply(Tuple3<String, String, String> key,
TimeWindow window, Iterable<MyEvent> input, Collector<MyEvent> out)
throws Exception {
                // This should print.
                System.out.println(key.toString());

                // Do nothing for now
            }
        })
        .uid("process").name("process")
        ;