@Override
    public byte[] serializeInternal(RowData rowData) {
        try {
            // noinspection unchecked
            Map<String, Object> outputMap = (Map<String, Object>) runtimeConverter.convert(rowData);
            return objectMapper.writeValueAsString(outputMap).getBytes(charset);
        } catch (Throwable t) {
            throw new RuntimeException(String.format("Could not serialize rowData '%s'.", rowData), t);
        }
    }
The string literal when handling mode for map null key LITERAL.
inlong-sort/sort-formats/format-rowdata/format-rowdata-json/src/main/java/org/apache/inlong/sort/formats/json/JsonRowDataSerializationSchema.java