@Test
    public void stringHeaderToConnect() {
        assertEquals(new SchemaAndValue(Schema.STRING_SCHEMA, "foo-bar-baz"), converter.toConnectHeader(TOPIC, "headerName", "{ \"schema\": { \"type\": \"string\" }, \"payload\": \"foo-bar-baz\" }".getBytes()));
    }
When schemas are disabled, fields are mapped to Connect maps.
connect/json/src/test/java/org/apache/kafka/connect/json/JsonConverterTest.java