code: public static Pair<InMemoryJarfile, String> loadAndUpgradeCatalogFromJar(InMemoryJarfile jarfile, boolean isXDCR)
          throws IOException
      {
          // Let VoltCompiler do a version check and upgrade the catalog on the fly.
          // I.e. jarfile may be modified.
          VoltCompiler compiler = new VoltCompiler(isXDCR);
          String upgradedFromVersion = compiler.upgradeCatalogAsNeeded(jarfile);
          return new Pair<>(jarfile, upgradedFromVersion);
      }
docs: Load a catalog from the InMemoryJarfile.
  
  @param jarfile
  @return Pair containing updated InMemoryJarFile and upgraded version (or null if it wasn't upgraded)
  @throws IOException if there is no version information in the catalog.