Talk mobile crash when starting new conversation – autocomplete returns empty user and null token triggers exception

When creating a new conversation in the Nextcloud Talk mobile app, the application crashes immediately on both Android and iOS.

This appears to be caused by two server-side issues in the autocomplete endpoint used when creating a new conversation.

1. filterExistingParticipants() is called with a null room token, causing a server exception.
2. The autocomplete API returns a malformed empty user entry with empty id and label, which causes the mobile client to crash when rendering the contact list.

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Steps to reproduce

1. Open Nextcloud Talk mobile app
2. Tap New conversation
3. App crashes immediately

The crash happens before any network request to create the room is completed.

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Server error

The autocomplete endpoint is called without a room token:

GET /ocs/v2.php/core/autocomplete/get?search=&itemType=call&shareTypes[]=0&shareTypes[]=1&shareTypes[]=4&shareTypes[]=7

This produces a server error in Talk:

OCA\Talk\Collaboration\Collaborators\Listener::filterExistingParticipants():
Argument nextcloud/spreed#1 ($token) must be of type string, null given

Server log excerpt:

OCA\Talk\Collaboration\Collaborators\Listener::filterExistingParticipants():
Argument nextcloud/spreed#1 ($token) must be of type string, null given,
called in apps/spreed/lib/Collaboration/Collaborators/Listener.php

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Malformed autocomplete entry

The autocomplete endpoint returns an invalid entry:

{
  "id": "",
  "label": "",
  "icon": "icon-user",
  "source": "users",
  "status": "",
  "subline": "",
  "shareWithDisplayNameUnique": ""
}

This entry appears as the first element in the response.

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Mobile crash

The Talk mobile client crashes when rendering this entry.

Android stack trace:

java.util.NoSuchElementException: Char sequence is empty.
    at kotlin.text.StringsKt___StringsKt.first(_Strings.kt:77)
    at com.nextcloud.talk.contacts.components.ContactsItemKt.ContactsItem

The crash happens because the UI attempts to call .first() on the empty label string.

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Working fix

Two fixes resolve the issue:

1. Guard against null or empty room tokens

Prevent filterExistingParticipants() from being called when the token is missing.

$itemId = $event->getItemId();
if ($itemId === null || $itemId === '' || $itemId === 'new') {
    return;
}

2. Filter malformed autocomplete entries

Remove results where label or shareWith are empty.

protected function filterMalformedUserResult(array $result): bool {
    $shareWith = trim((string)($result['value']['shareWith'] ?? ''));
    $label = trim((string)($result['label'] ?? ''));

    return $shareWith !== '' && $label !== '';
}

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Environment

Nextcloud version:

32.0.6

Talk app version:

22.0.9

Server:

Ubuntu 24.04
PHP 8.2
Redis enabled

Authentication:

OIDC (Authentik)

Reverse proxy:

Caddy
Cloudflare

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Additional notes

The malformed entry appears even when users are valid and display names are properly configured.

Example of valid entries returned in the same response:

{
  "id": "name@gmail.com",
  "label": "John Snow",
  "source": "users"
}

Only the first entry is malformed.

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Impact

This causes:

• Talk mobile apps to crash immediately
• New conversations cannot be created

Filtering malformed autocomplete results and guarding against null tokens resolves the issue.

Start with apps/spreed/lib/Collaboration/Collaborators/Listener.php and trace the autocomplete request for a new conversation, where the room token is absent. Verify the endpoint no longer raises the null-token exception and that results with empty labels or identifiers are excluded, then reproduce the new-conversation flow in Talk mobile to confirm valid contacts remain available.