@Override
    public Object parse(SourceData sourceData, int rowIndex, Context context) {
        Object indexObject = indexParser.parse(sourceData, rowIndex, context);
        if (indexObject == null) {
            return null;
        }

        int index = OperatorTools.parseBigDecimal(indexObject).intValue();
        if (index < 1 || index > exprParsers.size()) {
            return null;
        }

        return exprParsers.get(index - 1).parse(sourceData, rowIndex, context);
    }
EltFunction  ->  elt(index, expr1[, expr2, ...])
description:
- Return NULL if 'index' is NULL or out of range;
- Return the index-th('index' starts from 1) expression.
inlong-sdk/transform-sdk/src/main/java/org/apache/inlong/sdk/transform/process/function/string/EltFunction.java