private Object convertField(
            FieldToRowDataConverter fieldConverter,
            String fieldName,
            JsonNode field) throws IOException {
        if (field == null) {
            if (failOnMissingField) {
                throw new RuntimeException("Could not find field with name '" + fieldName + "'.");
            } else {
                return null;
            }
        } else {
            return fieldConverter.convert(getStringFromJsonNode(field));
        }
    }
Creates a runtime converter which assuming input object is not null.
inlong-sort/sort-formats/format-rowdata/format-rowdata-json/src/main/java/org/apache/inlong/sort/formats/json/FieldToRowDataConverters.java