code: def get_thumbnail_preset(self):
          
          if isinstance(self, ChannelNode):
              return format_presets.CHANNEL_THUMBNAIL
          elif isinstance(self, TopicNode):
              return format_presets.TOPIC_THUMBNAIL
          elif isinstance(self, VideoNode):
              return format_presets.VIDEO_THUMBNAIL
          elif isinstance(self, AudioNode):
              return format_presets.AUDIO_THUMBNAIL
          elif isinstance(self, DocumentNode):
              return format_presets.DOCUMENT_THUMBNAIL
          elif isinstance(self, ExerciseNode):
              return format_presets.EXERCISE_THUMBNAIL
          elif isinstance(self, HTML5AppNode):
              return format_presets.HTML5_THUMBNAIL
          else:
              return None
docs: Returns the format preset corresponding to this Node's type, or None if the node doesn't have a format preset.