old_contents: import uuid
  
  from django.db import migrations
  
  import waldur_core.core.fields
  
  
  def gen_uuid(apps, schema_editor):
      InvoiceItem = apps.get_model('invoices', 'InvoiceItem')
      for row in InvoiceItem.objects.all():
          row.uuid = uuid.uuid4().hex
          row.save(update_fields=['uuid'])
  
  
  class Migration(migrations.Migration):
  
      dependencies = [
          ('invoices', '0052_delete_servicedowntime'),
      ]
  
      operations = [
          migrations.AddField(
              model_name='invoiceitem',
              name='uuid',
              field=waldur_core.core.fields.UUIDField(null=True),
          ),
          migrations.RunPython(gen_uuid, elidable=True),
          migrations.AlterField(
              model_name='invoiceitem',
              name='uuid',
              field=waldur_core.core.fields.UUIDField(),
          ),
      ]
  
new_contents: import uuid
  
  from django.db import migrations, models
  
  import waldur_core.core.fields
  
  
  def gen_uuid(apps, schema_editor):
      InvoiceItem = apps.get_model('invoices', 'InvoiceItem')
      for row in InvoiceItem.objects.all():
          row.uuid = uuid.uuid4().hex
          row.save(update_fields=['uuid'])
  
  
  class Migration(migrations.Migration):
  
      dependencies = [
          ('invoices', '0052_delete_servicedowntime'),
      ]
  
      operations = [
          migrations.AddField(
              model_name='invoiceitem', name='uuid', field=models.UUIDField(null=True),
          ),
          migrations.RunPython(gen_uuid, elidable=True),
          migrations.AlterField(
              model_name='invoiceitem',
              name='uuid',
              field=waldur_core.core.fields.UUIDField(),
          ),
      ]
  
subject: Fix database migration script for UUID field in invoice item model.