Cannot add Avatar to Application Service

[krahlos]

Description

Calling PUT /_matrix/client/v3/profile/{userId}/avatar_url?user_id={userId} with an appservice token for a virtual user that has no existing profile row causes Synapse to crash with

TypeError: 'NoneType' object is not subscriptable` in `_check_profile_size

The upload step succeeds; only the profile PUT fails.

Steps to reproduce

1. Register an application service via app_service_config_files in homeserver.yml
2. User can send "Hello, world!" to private room on synapse
3. Upload picture with POST /_matrix/media/v3/upload?filename=<filename>&user_id=@<user>:<domain>
4. Call PUT /_matrix/client/v3/profile/@<user>:<domain>/avatar_url?user_id=@<user>:<domain> with the AS token
5. Synapse returns HTTP 500

Homeserver

private homeserver

Synapse Version

v1.151.0

Installation Method

Docker (matrixdotorg/synapse)

Database

PostgreSQL 18.1, single server, no SQLite migration

Workers

Single process

Platform

Ubuntu 24.04 (based on kernel 6.8), running in Docker container

Configuration

No response

Relevant log output

admin@my-homeserver:~$ docker logs matrix-synapse 2>&1 | grep -A20 "TypeError\|_check_profile_size\|ProfileField"
2026-04-16 20:24:50,818 - synapse.http.server - 147 - ERROR - PUT-21527 - Failed handle request via 'ProfileFieldRestServlet': <XForwardedForRequest at 0x70987d4a5950 method='PUT' uri='/_matrix/client/v3/profile/%40borgmatic%3Amatrix.private.org/avatar_url?user_id=%40borgmatic%3Amatrix.private.org' clientproto='HTTP/1.1' site='8008'>
Traceback (most recent call last):
  File "/usr/local/lib/python3.13/site-packages/synapse/http/server.py", line 335, in _async_render_wrapper
    callback_return = await self._async_render(request)
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/synapse/http/server.py", line 576, in _async_render
    callback_return = await raw_callback_return
                      ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.13/site-packages/synapse/rest/client/profile.py", line 212, in on_PUT
    await self.profile_handler.set_avatar_url(
        user, requester, new_value, by_admin=is_admin, propagate=propagate
    )
  File "/usr/local/lib/python3.13/site-packages/synapse/handlers/profile.py", line 364, in set_avatar_url
    await self.store.set_profile_avatar_url(target_user, avatar_url_to_set)
  File "/usr/local/lib/python3.13/site-packages/synapse/storage/databases/main/profile.py", line 435, in set_profile_avatar_url
    await self.db_pool.runInteraction(
        "set_profile_avatar_url", set_profile_avatar_url
    )
  File "/usr/local/lib/python3.13/site-packages/synapse/storage/database.py", line 1015, in runInteraction
    return await delay_cancellation(_runInteraction())
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
--
    self._check_profile_size(
    ~~~~~~~~~~~~~~~~~~~~~~~~^
        txn, user_id, ProfileFields.AVATAR_URL, new_avatar_url
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/usr/local/lib/python3.13/site-packages/synapse/storage/databases/main/profile.py", line 354, in _check_profile_size
    (row[0] - 1 if row[0] else 0)
                   ~~~^^^
TyError: 'NoneType' object is not subscriptable

Anything else that would be useful to know?

No response