docs: def get_value(self, dictionary):
          """
          Given the *incoming* primitive data, return the value for this field
          that should be validated and transformed to a native value.
          """
          if html.is_html_input(dictionary):
              # HTML forms will represent empty fields as '', and cannot
              # represent None or False values directly.
              if self.field_name not in dictionary:
                  if getattr(self.root, 'partial', False):
                      return empty
                  return self.default_empty_html
              ret = dictionary[self.field_name]
              if ret == '' and self.allow_null:
                  # If the field is blank, and null is a valid value then
                  # determine if we should use null instead.
                  return '' if getattr(self, 'allow_blank', False) else None
              elif ret == '' and not self.required:
                  # If the field is blank, and emptyness is valid then
                  # determine if we should use emptyness instead.
                  return '' if getattr(self, 'allow_blank', False) else empty
              return ret
          return dictionary.get(self.field_name, empty)