code: def run(self):
          
          path = self.path or CONTAINER_BUILD_JSON_PATH
          try:
              with open(path, 'r') as build_cfg_fd:
                  build_cfg_json = json.load(build_cfg_fd)
          except ValueError:
              self.log.error("couldn't decode json from file '%s'", path)
              return None
          except IOError:
              self.log.error("couldn't read json from file '%s'", path)
              return None
          else:
              return self.substitute_configuration(build_cfg_json)
docs: get json with build config from path