code: def validate(self):
          
          if not isinstance(self._data, dict):
              raise TypeError('freight forwarder configuration file must be a dict.')
  
          current_log_level = logger.get_level()
  
          if self._verbose:
              logger.set_level('DEBUG')
          else:
              logger.set_level('ERROR')
  
          logger.info('Starting configuration validation', extra={"formatter": 'config-start'})
  
          # copy config dict to allow config data to stay in its original state.
          config_data = self._data.copy()
  
          try:
              self._walk_tree(config_data, ROOT_SCHEME)
          except ConfigValidationException as e:
              e.log_error()
              raise
  
          logger.info("Config validation passed.", extra={'formatter': 'config-success'})
  
          logger.set_level(current_log_level)
docs: Validate the contents of the configuration file. Will return None if validation is successful or
          raise an error if not.