GET /api/hwid/devices/stats returns 500 (A159) when any device row has user_agent = NULL

Баг-репорты
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**Version:** 2.8.1 (also affects the 2.8.x stats code path)

**Symptom:** the dashboard HWID page fails with "get HWIDs Devices Stats Request failed with status code 500". Panel log:

ERROR [HwidUserDevicesService] Cannot read properties of null (reading ‘startsWith’)
ERROR [HttpExceptionFilter] Get hwid devices stats error - { code: ‘A159’, path: ‘/api/hwid/devices/stats’ }


**Root cause:** in `src/modules/hwid-user-devices/repositories/hwid-user-devices.repository.ts`, the stats query selects `SPLIT_PART("user_agent", '/', 1) AS app`. For rows where `user_agent IS NULL`, `SPLIT_PART` returns `NULL`, so `row.app` is `null`, and the aggregation then calls:

```ts
if (!app.startsWith('https:')) {

which throws TypeError: Cannot read properties of null (reading 'startsWith') → the whole stats endpoint 500s.

Repro:

  1. Have at least one row in hwid_user_devices with user_agent IS NULL (e.g. a device registered via POST /api/hwid/devices without the optional userAgent field).
  2. GET /api/hwid/devices/stats → 500, error code A159.

Suggested fix: null-guard the aggregation, e.g. const app = row.app ?? 'Unknown'; (or COALESCE("user_agent", 'Unknown') in the SQL). userAgent is optional in the create-device API, so NULL rows are a legal state.

Workaround for anyone hitting this: UPDATE hwid_user_devices SET user_agent = 'Unknown' WHERE user_agent IS NULL;

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