private void init() throws IOException {
    myMap = PersistentMapBuilder.newBuilder(myFile.toPath(), mySubIndexerTypeDescriptor, EnumeratorIntegerDescriptor.INSTANCE)
      //.wantNonNegativeIntegralValues()
    .build();
      // getSize/remove are required here
    File nextVersionFile = getNextVersionFile(myFile);
    String intValue = nextVersionFile.exists() ? FileUtil.loadFile(nextVersionFile, StandardCharsets.UTF_8) : String.valueOf(1);
    try {
      myNextVersion = Integer.parseInt(intValue);
      myWrittenNextVersion = myNextVersion;
    }
    catch (NumberFormatException e) {
      throw new IOException("Invalid next version format " + intValue);
    }
  }
private void init()