stream WHERE excludes rows with null value

[big-andy-coates]

The following QTT test should pass:

{
      "name": "filtered stream row with null value",
      "statements": [
        "CREATE STREAM INPUT (ID INT KEY, NAME STRING) WITH (kafka_topic='test_topic', value_format='JSON');",
        "CREATE STREAM OUTPUT AS SELECT * FROM INPUT WHERE NAME IS NULL;"
      ],
      "inputs": [
        {"topic": "test_topic", "key": 1, "value": null},
        {"topic": "test_topic", "key": 2, "value": {"NAME": null}},
        {"topic": "test_topic", "key": 3, "value": {"NAME": "bob"}}
      ],
      "outputs": [
        {"topic": "OUTPUT", "key": 1, "value": null},
        {"topic": "OUTPUT", "key": 2, "value": {"NAME": null}}
      ]
    }

Because the value of NAME in the first row should be null, i.e. it has no value. Yet this row is filtered out. This is wrong.