code: def get_backend_type(self, location):
          # type: (str) -> Optional[Type[VersionControl]]
          
          for vc_type in self._registry.values():
              if vc_type.controls_location(location):
                  logger.debug('Determine that %s uses VCS: %s',
                               location, vc_type.name)
                  return vc_type
          return None
docs: Return the type of the version control backend if found at given
          location, e.g. vcs.get_backend_type('/path/to/vcs/checkout')