@Test
    public void nullSchemaAndMapToJson() {
        // This still needs to do conversion of data, null schema means "anything goes". Make sure we mix and match
        // types to verify conversion still works.
        Map<String, Object> input = new HashMap<>();
        input.put("key1", 12);
        input.put("key2", "string");
        input.put("key3", true);
        JsonNode converted = parse(converter.fromConnectData(TOPIC, null, input));
        validateEnvelopeNullSchema(converted);
        assertTrue(converted.get(JsonSchema.ENVELOPE_SCHEMA_FIELD_NAME).isNull());
        assertEquals(JsonNodeFactory.instance.objectNode().put("key1", 12).put("key2", "string").put("key3", true),
                converted.get(JsonSchema.ENVELOPE_PAYLOAD_FIELD_NAME));
    }
When schemas are disabled, fields are mapped to Connect maps.
connect/json/src/test/java/org/apache/kafka/connect/json/JsonConverterTest.java