code: def _validate_value(self, proposal):
      if "" in proposal["value"]:
          raise TraitError(
              "The value of a TagsInput widget cannot contain blank strings"
          )
  
      if len(self.allowed_tags) == 0:
          return proposal["value"]
  
      for tag_value in proposal["value"]:
          if tag_value not in self.allowed_tags:
              raise TraitError(
                  "Tag value {} is not allowed, allowed tags are {}".format(
                      tag_value, self.allowed_tags
                  )
              )
  
      return proposal["value"]
  
imports: from traitlets import CaselessStrEnum, CInt, CFloat, Bool, Unicode, List, TraitError, validate
  from .widget_description import DescriptionWidget
  from .valuewidget import ValueWidget
  from .widget_core import CoreWidget
  from .widget import register
  from .trait_types import Color, NumberFormat
label_desc: Use image node_id 1 for calling the TagsInputBase obj's underlying member method code with example usage: obj._validate_value(proposal) and returns: proposal, proposal