code: protected void fillIndexFromByteBuffer() {
          indexBuffer.rewind();
          for (int i = 0; i < numberOfChunks; i++) {
              maxKeyPerChunk[i] = new byte[keySize];
              indexBuffer.get(maxKeyPerChunk[i]);
              if (KeyUtils.isNull(maxKeyPerChunk[i]) && i > 0) {
                  filledUpTo = i - 1;
                  break;
              }
          }
      }
docs: loads the index from the {@link MappedByteBuffer}