@Test
    public void nullSchemaAndMapNonStringKeysToJson() {
        // 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<Object, Object> input = new HashMap<>();
        input.put("string", 12);
        input.put(52, "string");
        input.put(false, true);
        JsonNode converted = parse(converter.fromConnectData(TOPIC, null, input));
        validateEnvelopeNullSchema(converted);
        assertTrue(converted.get(JsonSchema.ENVELOPE_SCHEMA_FIELD_NAME).isNull());
        assertTrue(converted.get(JsonSchema.ENVELOPE_PAYLOAD_FIELD_NAME).isArray());
        ArrayNode payload = (ArrayNode) converted.get(JsonSchema.ENVELOPE_PAYLOAD_FIELD_NAME);
        assertEquals(3, payload.size());
        Set<JsonNode> payloadEntries = new HashSet<>();
        for (JsonNode elem : payload)
            payloadEntries.add(elem);
        assertEquals(new HashSet<>(Arrays.asList(JsonNodeFactory.instance.arrayNode().add("string").add(12),
                        JsonNodeFactory.instance.arrayNode().add(52).add("string"),
                        JsonNodeFactory.instance.arrayNode().add(false).add(true))),
                payloadEntries
        );
    }
When schemas are disabled, fields are mapped to Connect maps.
connect/json/src/test/java/org/apache/kafka/connect/json/JsonConverterTest.java