old_contents: from django import forms
  from django.core.exceptions import ValidationError
  
  from .models import NewsLink, Startup, Tag
  
  
  class NewsLinkForm(forms.ModelForm):
      class Meta:
          model = NewsLink
          fields = '__all__'
  
  
  class StartupForm(forms.ModelForm):
      class Meta:
          model = Startup
          fields = '__all__'
  
  
  class TagForm(forms.ModelForm):
      class Meta:
          model = Tag
          fields = '__all__'
  
      def clean_name(self):
          return self.cleaned_data['name'].lower()
  
      def clean_slug(self):
          new_slug = (
              self.cleaned_data['slug'].lower())
          if new_slug == 'create':
              raise ValidationError(
                  'Slug may not be "create".')
          return new_slug
  
new_contents: from django import forms
  from django.core.exceptions import ValidationError
  
  from .models import NewsLink, Startup, Tag
  
  
  class NewsLinkForm(forms.ModelForm):
      class Meta:
          model = NewsLink
          fields = '__all__'
  
  
  class StartupForm(forms.ModelForm):
      class Meta:
          model = Startup
          fields = '__all__'
  
      def clean_slug(self):
          new_slug = (
              self.cleaned_data['slug'].lower())
          if new_slug == 'create':
              raise ValidationError(
                  'Slug may not be "create".')
          return new_slug
  
  
  class TagForm(forms.ModelForm):
      class Meta:
          model = Tag
          fields = '__all__'
  
      def clean_name(self):
          return self.cleaned_data['name'].lower()
  
      def clean_slug(self):
          new_slug = (
              self.cleaned_data['slug'].lower())
          if new_slug == 'create':
              raise ValidationError(
                  'Slug may not be "create".')
          return new_slug
  
subject: Implement StartupForm clean_slug method.