code: def _get_metadata_model(name=None):
      
      if name is not None:
          try:
              return registry[name]
          except KeyError:
              if len(registry) == 1:
                  valid_names = 'Try using the name "%s" or simply leaving it '\
                                'out altogether.' % list(registry)[0]
              else:
                  valid_names = "Valid names are " + ", ".join(
                      '"%s"' % k for k in list(registry))
              raise Exception(
                  "Metadata definition with name \"%s\" does not exist.\n%s" % (
                      name, valid_names))
      else:
          assert len(registry) == 1, \
              "You must have exactly one Metadata class, if using " \
              "get_metadata() without a 'name' parameter."
          return list(registry.values())[0]
docs: Find registered Metadata object.