@Override
    public boolean nextRecord() {
        if (pageRecordCount <= readCount) {
            return false;
        }

        if (readCount > 0) {
            // advance position excepting the first record
            int lastRecordSize = pageSlice.getInt(position);
            position += lastRecordSize;
        }

        readCount++;
        pageSlice.getBytes(position + 4, nullBitSet, 0, nullBitSet.length);

        return true;
    }
Returns a JSON value at the specified column.

@param columnIndex  the index the column to get the JSON value
@return the JSON value
embulk-core/src/main/java/org/embulk/spi/PageReaderImpl.java