code: def validate(self) -> None:
      exceptions: list[ValidationError] = []
      layer_id: Optional[int] = self._properties.get("layer")
      short_descr: str = self._properties.get("short_descr", "")
  
      # Validate/populate model exists
      self._model = AnnotationDAO.find_by_id(self._model_id)
      if not self._model:
          raise AnnotationNotFoundError()
      # Validate/populate layer exists
      if layer_id:
          annotation_layer = AnnotationLayerDAO.find_by_id(layer_id)
          if not annotation_layer:
              raise AnnotationLayerNotFoundError()
          self._properties["layer"] = annotation_layer
  
          # Validate short descr uniqueness on this layer
          if not AnnotationDAO.validate_update_uniqueness(
              layer_id,
              short_descr,
              annotation_id=self._model_id,
          ):
              exceptions.append(AnnotationUniquenessValidationError())
      else:
          self._properties["layer"] = self._model.layer
  
      # validate date time sanity
      start_dttm: Optional[datetime] = self._properties.get(
          "start_dttm"
      )
      end_dttm: Optional[datetime] = self._properties.get("end_dttm")
  
      if start_dttm and end_dttm and end_dttm < start_dttm:
          exceptions.append(AnnotationDatesValidationError())
  
      if exceptions:
          raise AnnotationInvalidError(exceptions=exceptions)
  
file_path: superset/superset/commands/annotation_layer/annotation/update.py
imports: import logging
  from datetime import datetime
  from typing import Any, Optional
  from flask_appbuilder.models.sqla import Model
  from marshmallow import ValidationError
  from superset.commands.annotation_layer.annotation.exceptions import AnnotationDatesValidationError, AnnotationInvalidError, AnnotationNotFoundError, AnnotationUniquenessValidationError, AnnotationUpdateFailedError
  from superset.commands.annotation_layer.exceptions import AnnotationLayerNotFoundError
  from superset.commands.base import BaseCommand
  from superset.daos.annotation_layer import AnnotationDAO, AnnotationLayerDAO
  from superset.daos.exceptions import DAOUpdateFailedError
  from superset.models.annotations import Annotation
label_desc: Use image node_id 3 for calling the UpdateAnnotationCommand obj's underlying member method code with example usage: obj.validate() without return types