code: private boolean next() throws IOException {
      if (valuesRead >= endOfPageValueCount) {
        if (valuesRead >= totalValueCount) {
          // How do we get here? Throw end of stream exception?
          return false;
        }
        readPage();
      }
      ++valuesRead;
      // TODO: Don't read for flat schemas
      //repetitionLevel = repetitionLevelColumn.nextInt();
      return definitionLevelColumn.nextInt() == maxDefLevel;
    }
docs: Advances to the next value. Returns true if the value is non-null.