docs: def value_from_datadict(self, data, files, name):
          """
          Given a dictionary of data and this widget's name, returns the value
          of this widget. Returns None if it's not provided.
          """
          value = super(FileSizeWidget, self).value_from_datadict(data, files, name)
          if value not in EMPTY_VALUES:
              try:
                  return parse_size(value)
              except ValueError:
                  pass
          return value