code: def bundle_models(models):
      
      custom_models = _get_custom_models(models)
      if custom_models is None:
          return None
  
      key = calc_cache_key(custom_models)
      bundle = _bundle_cache.get(key, None)
      if bundle is None:
          try:
              _bundle_cache[key] = bundle = _bundle_models(custom_models)
          except CompilationError as error:
              print("Compilation failed:", file=sys.stderr)
              print(str(error), file=sys.stderr)
              sys.exit(1)
      return bundle
docs: Create a bundle of selected `models`.