@Test
    public void noSchemaToConnect() {
        Map<String, Boolean> props = Collections.singletonMap("schemas.enable", false);
        converter.configure(props, true);
        assertEquals(new SchemaAndValue(null, true), converter.toConnectData(TOPIC, "true".getBytes()));
    }
When schemas are disabled, fields are mapped to Connect maps.
connect/json/src/test/java/org/apache/kafka/connect/json/JsonConverterTest.java