Django Timefield(default=<TimeDelta>) gives unhelpful diagnostics

(Be warned, I am a novice and this may be a novice mistake):

I mistakenly added a TimeField instead of a DurationField to my model. I was forced to give it a default value and chose TimeDelta(minutes=30). The makemigration worked, but the migrate command crashed with very unhelpful diagnostics, not even indicating which field caused the problem.

I'm hoping that this lack of diagnostics could be improved, to at least point to the database column that caused the problem?

Thanks in advance for all the good stuff you do :-)
Simon Lambourn.

Output from manage.py migrate:

Operations to perform:
  Apply all migrations: admin, auth, contenttypes, kitten, sessions
Running migrations:
  Applying kitten.0010_auto_20200428_0957...Traceback (most recent call last):
  File "manage.py", line 22, in <module>
    execute_from_command_line(sys.argv)
  File "/usr/lib/python3/dist-packages/django/core/management/__init__.py", line 364, in execute_from_command_line
    utility.execute()
  File "/usr/lib/python3/dist-packages/django/core/management/__init__.py", line 356, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/usr/lib/python3/dist-packages/django/core/management/base.py", line 283, in run_from_argv
    self.execute(*args, **cmd_options)
  File "/usr/lib/python3/dist-packages/django/core/management/base.py", line 330, in execute
    output = self.handle(*args, **options)
  File "/usr/lib/python3/dist-packages/django/core/management/commands/migrate.py", line 204, in handle
    fake_initial=fake_initial,
  File "/usr/lib/python3/dist-packages/django/db/migrations/executor.py", line 115, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "/usr/lib/python3/dist-packages/django/db/migrations/executor.py", line 145, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "/usr/lib/python3/dist-packages/django/db/migrations/executor.py", line 244, in apply_migration
    state = migration.apply(state, schema_editor)
  File "/usr/lib/python3/dist-packages/django/db/migrations/migration.py", line 129, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "/usr/lib/python3/dist-packages/django/db/migrations/operations/fields.py", line 88, in database_forwards
    field,
  File "/usr/lib/python3/dist-packages/django/db/backends/sqlite3/schema.py", line 240, in add_field
    self._remake_table(model, create_field=field)
  File "/usr/lib/python3/dist-packages/django/db/backends/sqlite3/schema.py", line 115, in _remake_table
    self.effective_default(create_field)
  File "/usr/lib/python3/dist-packages/django/db/backends/base/schema.py", line 245, in effective_default
    default = field.get_db_prep_save(default, self.connection)
  File "/usr/lib/python3/dist-packages/django/db/models/fields/__init__.py", line 770, in get_db_prep_save
    prepared=False)
  File "/usr/lib/python3/dist-packages/django/db/models/fields/__init__.py", line 2281, in get_db_prep_value
    value = self.get_prep_value(value)
  File "/usr/lib/python3/dist-packages/django/db/models/fields/__init__.py", line 2276, in get_prep_value
    return self.to_python(value)
  File "/usr/lib/python3/dist-packages/django/db/models/fields/__init__.py", line 2250, in to_python
    parsed = parse_time(value)
  File "/usr/lib/python3/dist-packages/django/utils/dateparse.py", line 76, in parse_time
    match = time_re.match(value)
TypeError: expected string or bytes-like object

ProblemType: Bug
DistroRelease: Ubuntu 19.10
Package: python3-django 1:1.11.22-1ubuntu1.3
ProcVersionSignature: Ubuntu 5.3.0-46.38-generic 5.3.18
Uname: Linux 5.3.0-46-generic x86_64
ApportVersion: 2.20.11-0ubuntu8.8
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Tue Apr 28 09:59:25 2020
PackageArchitecture: all
SourcePackage: python-django
UpgradeStatus: Upgraded to eoan on 2019-10-23 (187 days ago)