docs: def _write_field(self, value):
          """
          Write a single field to the destination file.
  
          :param T value: The value of the field.
          """
          class_name = str(value.__class__)
          if class_name not in self.handlers:
              raise ValueError('No handler has been registered for class: {0!s}'.format(class_name))
          handler = self.handlers[class_name]
          handler(value, self._file)