content: from django.db import migrations, models
  
  
  def set_null_values(apps, schema_editor):
      """
      Replace empty strings with null values.
      """
      FHRPGroup = apps.get_model('ipam', 'FHRPGroup')
      IPAddress = apps.get_model('ipam', 'IPAddress')
      db_alias = schema_editor.connection.alias
  
      FHRPGroup.objects.using(db_alias).filter(auth_type='').update(auth_type=None)
      IPAddress.objects.using(db_alias).filter(role='').update(role=None)
  
  
  class Migration(migrations.Migration):
      dependencies = [
          ('ipam', '0072_prefix_cached_relations'),
      ]
  
      operations = [
          migrations.AlterField(
              model_name='fhrpgroup',
              name='auth_type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='ipaddress',
              name='role',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.RunPython(code=set_null_values, reverse_code=migrations.RunPython.noop),
      ]
  