old_contents: 
  from django import forms
  from django.forms import widgets
  
  from . import models
  
  
  class ThreadCreateForm(forms.ModelForm):
  
      class Meta:
          model = models.Thread
          fields = ['title']
  
  
  class MessageCreateForm(forms.ModelForm):
  
      class Meta:
          model = models.Message
          fields = ['body']
  
  
  class TagFilterForm(forms.Form):
      tag = forms.ModelMultipleChoiceField(
          queryset=models.Tag.objects.all(),
          required=True,
          widget=widgets.CheckboxSelectMultiple
      )
new_contents: 
  from django import forms
  from django.forms import widgets
  
  from . import models
  
  
  class ThreadCreateForm(forms.ModelForm):
  
      class Meta:
          model = models.Thread
          fields = ['title']
  
  
  class MessageCreateForm(forms.ModelForm):
  
      class Meta:
          model = models.Message
          fields = ['body']
  
  
  class TagFilterForm(forms.Form):
      tag = forms.ModelMultipleChoiceField(
          queryset=models.Tag.objects.all(),
          required=False,
          widget=widgets.CheckboxSelectMultiple
      )
  
subject: Mark tags as not required in filter form