@SuppressWarnings("unchecked")
    public T nullLiteral(String nullLiteral) {
        checkNotNull(nullLiteral);
        internalProperties.putString(FORMAT_NULL_LITERAL, nullLiteral);
        return (T) this;
    }
Sets the null literal string that is interpreted as a null value
(disabled by default).

@param nullLiteral null literal (e.g. "null" or "n/a")
inlong-sort/sort-formats/format-common/src/main/java/org/apache/inlong/sort/formats/base/TextFormatDescriptor.java