content: import timezone_field.fields
  from django.db import migrations, models
  
  
  def set_null_values(apps, schema_editor):
      """
      Replace empty strings with null values.
      """
      Cable = apps.get_model('dcim', 'Cable')
      ConsolePort = apps.get_model('dcim', 'ConsolePort')
      ConsolePortTemplate = apps.get_model('dcim', 'ConsolePortTemplate')
      ConsoleServerPort = apps.get_model('dcim', 'ConsoleServerPort')
      ConsoleServerPortTemplate = apps.get_model('dcim', 'ConsoleServerPortTemplate')
      Device = apps.get_model('dcim', 'Device')
      DeviceType = apps.get_model('dcim', 'DeviceType')
      FrontPort = apps.get_model('dcim', 'FrontPort')
      Interface = apps.get_model('dcim', 'Interface')
      InterfaceTemplate = apps.get_model('dcim', 'InterfaceTemplate')
      ModuleType = apps.get_model('dcim', 'ModuleType')
      PowerFeed = apps.get_model('dcim', 'PowerFeed')
      PowerOutlet = apps.get_model('dcim', 'PowerOutlet')
      PowerOutletTemplate = apps.get_model('dcim', 'PowerOutletTemplate')
      PowerPort = apps.get_model('dcim', 'PowerPort')
      PowerPortTemplate = apps.get_model('dcim', 'PowerPortTemplate')
      Rack = apps.get_model('dcim', 'Rack')
      RackType = apps.get_model('dcim', 'RackType')
      RearPort = apps.get_model('dcim', 'RearPort')
      Site = apps.get_model('dcim', 'Site')
      db_alias = schema_editor.connection.alias
  
      Cable.objects.using(db_alias).filter(length_unit='').update(length_unit=None)
      Cable.objects.using(db_alias).filter(type='').update(type=None)
      ConsolePort.objects.using(db_alias).filter(cable_end='').update(cable_end=None)
      ConsolePort.objects.using(db_alias).filter(type='').update(type=None)
      ConsolePortTemplate.objects.using(db_alias).filter(type='').update(type=None)
      ConsoleServerPort.objects.using(db_alias).filter(cable_end='').update(cable_end=None)
      ConsoleServerPort.objects.using(db_alias).filter(type='').update(type=None)
      ConsoleServerPortTemplate.objects.using(db_alias).filter(type='').update(type=None)
      Device.objects.using(db_alias).filter(airflow='').update(airflow=None)
      Device.objects.using(db_alias).filter(face='').update(face=None)
      DeviceType.objects.using(db_alias).filter(airflow='').update(airflow=None)
      DeviceType.objects.using(db_alias).filter(subdevice_role='').update(subdevice_role=None)
      DeviceType.objects.using(db_alias).filter(weight_unit='').update(weight_unit=None)
      FrontPort.objects.using(db_alias).filter(cable_end='').update(cable_end=None)
      Interface.objects.using(db_alias).filter(cable_end='').update(cable_end=None)
      Interface.objects.using(db_alias).filter(mode='').update(mode=None)
      Interface.objects.using(db_alias).filter(poe_mode='').update(poe_mode=None)
      Interface.objects.using(db_alias).filter(poe_type='').update(poe_type=None)
      Interface.objects.using(db_alias).filter(rf_channel='').update(rf_channel=None)
      Interface.objects.using(db_alias).filter(rf_role='').update(rf_role=None)
      InterfaceTemplate.objects.using(db_alias).filter(poe_mode='').update(poe_mode=None)
      InterfaceTemplate.objects.using(db_alias).filter(poe_type='').update(poe_type=None)
      InterfaceTemplate.objects.using(db_alias).filter(rf_role='').update(rf_role=None)
      ModuleType.objects.using(db_alias).filter(airflow='').update(airflow=None)
      ModuleType.objects.using(db_alias).filter(weight_unit='').update(weight_unit=None)
      PowerFeed.objects.using(db_alias).filter(cable_end='').update(cable_end=None)
      PowerOutlet.objects.using(db_alias).filter(cable_end='').update(cable_end=None)
      PowerOutlet.objects.using(db_alias).filter(feed_leg='').update(feed_leg=None)
      PowerOutlet.objects.using(db_alias).filter(type='').update(type=None)
      PowerOutletTemplate.objects.using(db_alias).filter(feed_leg='').update(feed_leg=None)
      PowerOutletTemplate.objects.using(db_alias).filter(type='').update(type=None)
      PowerPort.objects.using(db_alias).filter(cable_end='').update(cable_end=None)
      PowerPort.objects.using(db_alias).filter(type='').update(type=None)
      PowerPortTemplate.objects.using(db_alias).filter(type='').update(type=None)
      Rack.objects.using(db_alias).filter(airflow='').update(airflow=None)
      Rack.objects.using(db_alias).filter(form_factor='').update(form_factor=None)
      Rack.objects.using(db_alias).filter(outer_unit='').update(outer_unit=None)
      Rack.objects.using(db_alias).filter(weight_unit='').update(weight_unit=None)
      RackType.objects.using(db_alias).filter(outer_unit='').update(outer_unit=None)
      RackType.objects.using(db_alias).filter(weight_unit='').update(weight_unit=None)
      RearPort.objects.using(db_alias).filter(cable_end='').update(cable_end=None)
      Site.objects.using(db_alias).filter(time_zone='').update(time_zone=None)
  
  
  class Migration(migrations.Migration):
      dependencies = [
          ('dcim', '0193_poweroutlet_color'),
      ]
  
      operations = [
          migrations.AlterField(
              model_name='cable',
              name='length_unit',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='cable',
              name='type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='consoleport',
              name='cable_end',
              field=models.CharField(blank=True, max_length=1, null=True),
          ),
          migrations.AlterField(
              model_name='consoleport',
              name='type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='consoleporttemplate',
              name='type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='consoleserverport',
              name='cable_end',
              field=models.CharField(blank=True, max_length=1, null=True),
          ),
          migrations.AlterField(
              model_name='consoleserverport',
              name='type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='consoleserverporttemplate',
              name='type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='device',
              name='airflow',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='device',
              name='face',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='devicetype',
              name='airflow',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='devicetype',
              name='subdevice_role',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='devicetype',
              name='weight_unit',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='frontport',
              name='cable_end',
              field=models.CharField(blank=True, max_length=1, null=True),
          ),
          migrations.AlterField(
              model_name='interface',
              name='cable_end',
              field=models.CharField(blank=True, max_length=1, null=True),
          ),
          migrations.AlterField(
              model_name='interface',
              name='mode',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='interface',
              name='poe_mode',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='interface',
              name='poe_type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='interface',
              name='rf_channel',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='interface',
              name='rf_role',
              field=models.CharField(blank=True, max_length=30, null=True),
          ),
          migrations.AlterField(
              model_name='interfacetemplate',
              name='poe_mode',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='interfacetemplate',
              name='poe_type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='interfacetemplate',
              name='rf_role',
              field=models.CharField(blank=True, max_length=30, null=True),
          ),
          migrations.AlterField(
              model_name='moduletype',
              name='airflow',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='moduletype',
              name='weight_unit',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='powerfeed',
              name='cable_end',
              field=models.CharField(blank=True, max_length=1, null=True),
          ),
          migrations.AlterField(
              model_name='poweroutlet',
              name='cable_end',
              field=models.CharField(blank=True, max_length=1, null=True),
          ),
          migrations.AlterField(
              model_name='poweroutlet',
              name='feed_leg',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='poweroutlet',
              name='type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='poweroutlettemplate',
              name='feed_leg',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='poweroutlettemplate',
              name='type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='powerport',
              name='cable_end',
              field=models.CharField(blank=True, max_length=1, null=True),
          ),
          migrations.AlterField(
              model_name='powerport',
              name='type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='powerporttemplate',
              name='type',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='rack',
              name='airflow',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='rack',
              name='form_factor',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='rack',
              name='outer_unit',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='rack',
              name='weight_unit',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='racktype',
              name='outer_unit',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='racktype',
              name='weight_unit',
              field=models.CharField(blank=True, max_length=50, null=True),
          ),
          migrations.AlterField(
              model_name='rearport',
              name='cable_end',
              field=models.CharField(blank=True, max_length=1, null=True),
          ),
          migrations.AlterField(
              model_name='site',
              name='time_zone',
              field=timezone_field.fields.TimeZoneField(blank=True, null=True),
          ),
          migrations.RunPython(code=set_null_values, reverse_code=migrations.RunPython.noop),
      ]
  