docs: def value_from_datadict(self, data, files, name):
          """Returns uploaded file from serialized value."""
          upload = super(StickyUploadWidget, self).value_from_datadict(data, files, name)
          if upload is not None:
              # File was posted or cleared as normal
              return upload
          else:
              # Try the hidden input
              hidden_name = self.get_hidden_name(name)
              value = data.get(hidden_name, None)
              if value is not None:
                  upload = open_stored_file(value, self.url)
                  if upload is not None:
                      setattr(upload, '_seralized_location', value)
          return upload