@Test
    public void intToJson() {
        JsonNode converted = parse(converter.fromConnectData(TOPIC, Schema.INT32_SCHEMA, 12));
        validateEnvelope(converted);
        assertEquals(parse("{ \"type\": \"int32\", \"optional\": false }"), converted.get(JsonSchema.ENVELOPE_SCHEMA_FIELD_NAME));
        assertEquals(12, converted.get(JsonSchema.ENVELOPE_PAYLOAD_FIELD_NAME).intValue());
    }
When schemas are disabled, fields are mapped to Connect maps.
connect/json/src/test/java/org/apache/kafka/connect/json/JsonConverterTest.java