old_contents: from django.db import models
  
  from .fields import ListTextField
  
  
  class TwoModularColumnsMixin(models.Model):
      sidebar_left = ListTextField()
      sidebar_right = ListTextField()
  
      class Meta:
          abstract = True
  
new_contents: from django.db import models
  
  from .fields import ListTextField
  
  
  class TwoModularColumnsMixin(models.Model):
      sidebar_left = ListTextField(
          blank=True,
          null=True,
      )
      sidebar_right = ListTextField(
          lank=True,
          null=True,
      )
  
      class Meta:
          abstract = True
  
subject: Add null and blank to sidebars