code: def include(self):
          
          include_param = self.qs.get('include', [])
  
          if current_app.config.get('MAX_INCLUDE_DEPTH') is not None:
              for include_path in include_param:
                  if len(include_path.split('.')) > current_app.config['MAX_INCLUDE_DEPTH']:
                      raise InvalidInclude("You can't use include through more than {} relationships"
                                           .format(current_app.config['MAX_INCLUDE_DEPTH']))
  
          return include_param.split(',') if include_param else []
docs: Return fields to include
  
          :return list: a list of include information