Hi, I'm super new and trying out the SQL client. Why would all watermarks be

<NULL>

? I have this kafka source:

CREATE TABLE kafka_source (
            id INT,
            name STRING,
            ts TIMESTAMP(3),
            WATERMARK FOR ts AS ts 
        ) WITH (
            'connector' = 'kafka',
            'properties.bootstrap.servers' = 'kafka:9092',
            'properties.group.id' = 'test',
            'scan.startup.mode' = 'earliest-offset',
            'topic' ='source',
            'value.format' = 'json'
        );

The WATERMARK seems to enable a TUMBLE window

SELECT * FROM TABLE(
   TUMBLE(TABLE kafka_source, DESCRIPTOR(ts), INTERVAL '5' SECONDS));

I can insert fine:

INSERT INTO kafka_source
                      VALUES (1, 'matt', CURRENT_TIMESTAMP);

But the watermarks are all null. i.e.

SELECT CURRENT_WATERMARK(ts) from kafka_source;

Opens a window, with a Table, and all the values are

<NULL>

. Why would all watermarks be

<NULL>

?