code: def value_from_datadict(self, data, files, name):
          
          clear = self.checkbox.value_from_datadict(data, files, self.clear_checkbox_name(name))
          if clear:
              return self.empty_value
          return self.widget.value_from_datadict(data, files, name)
docs: If the clear checkbox is checked returns the configured empty value,
          completely ignoring the original input.