code: def add(self, key, value):
          
          if isinstance(value, list):
              for val in value:
                  self.appendlist(key, val)
          else:
              self.appendlist(key, value)
docs: Method to accept a list of values and append to flat list.
          QueryDict.appendlist(), if given a list, will append the list,
          which creates nested lists. In most cases, we want to be able
          to pass in a list (for convenience) but have it appended into
          a flattened list.
          TODO: Possibly throw an error if add() is used on a non-list param.