code: @Restricted(NoExternalUse.class)
      @CheckForNull
      public VersionNumber getCurrentLevel() {
          VersionNumber from = new VersionNumber("1.0");
          File state = getUpdateStateFile();
          if (state.exists()) {
              try {
                  from = new VersionNumber(defaultIfBlank(readFileToString(state), "1.0").trim());
              } catch (IOException ex) {
                  LOGGER.log(Level.SEVERE, "Cannot read the current version file", ex);
                  return null;
              }
          }
          return from;
      }
docs: What is the version the upgrade wizard has run the last time and upgraded to?.
  If {@link #getUpdateStateFile()} is missing, presumes the baseline is 1.0
  @return Current baseline. {@code null} if it cannot be retrieved.