@Test
    public void decimalToJsonWithoutSchema() {
        assertThrows(
            DataException.class,
            () -> converter.fromConnectData(TOPIC, null, new BigDecimal(new BigInteger("156"), 2)),
            "expected data exception when serializing BigDecimal without schema");
    }
When schemas are disabled, fields are mapped to Connect maps.
connect/json/src/test/java/org/apache/kafka/connect/json/JsonConverterTest.java