Kafka JSON Spec Does Propagates DH Nulls Instead of JSON Null

[nbauernfeind]

To reproduce:

import random
from deephaven import kafka_producer as pk

source_group = time_table("PT00:00:00.1").update(
    formulas=["X = (int) random.randint(1, 5)", "Y = X == 3 ? null : i"]
)

write_topic_group = pk.produce(
    source_group,
    {"bootstrap.servers": "redpanda:9092"},
    "time-topic_group",
    pk.json_spec(["X"]),
    pk.json_spec(
        [
            "X",
            "Y",
        ]
    ),
    True,
)

This produces deephaven null values to the stream instead of real null values; see redpanda snapshot below:

(You will have to ignore that X == "3", Y == non-null instance in my image; that was because I [accidentally] had more than one producer running on the same topic at the time of the shot.)