code: public boolean nextIsNull(long currentRow) throws IOException {
      if (present != null) {
        seekToPresentRow(currentRow);
        valuePresent = present.next() == 1;
        if (valuePresent) {
          // Adjust numNonNulls so we know how many non-null values we'll need to skip if skip is
          // called
          numNonNulls++;
        } else {
          if (currentRow == previousRow + 1) {
            // if currentRow = previousRow + 1, and the value is null this is equivalent to going to the
            // next row.  if there's a series of nulls this prevents us from calling skipRows when
            // the next non-null value is fetched
            previousRow++;
          }
        }
      }
  
      return !valuePresent;
    }
docs: Returns whether or not the value corresponding to currentRow is null, suitable for calling
  from outside
  
  @param currentRow
  @return
  @throws IOException