Cron mail sync failed: `getUid()` on null

Steps to reproduce

1. Wait for cron to run

Expected behavior

No error

Actual behavior

Error

Mail app version

5.1.2

Nextcloud version

30.0.11

Mailserver or service

No response

Operating system

No response

PHP engine version

PHP 8.3

Nextcloud memory caching

Redis

Web server

Apache (supported)

Database

MariaDB

Additional info

{
  "reqId": "WVuQI7DCyaWsM8VSqVPH",
  "level": 3,
  "time": "2025-06-05T06:54:04+02:00",
  "remoteAddr": "",
  "user": "--",
  "app": "mail",
  "method": "",
  "url": "--",
  "message": "Cron mail sync failed for account 35",
  "userAgent": "--",
  "version": "30.0.11.1",
  "exception": {
    "Exception": "OCA\\Mail\\Exception\\ServiceException",
    "Message": "Sync failed for 35:INBOX: Call to a member function getUid() on null",
    "Code": 0,
    "Trace": [
      {
        "file": "/var/www/nextcloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php",
        "line": 133,
        "function": "sync",
        "class": "OCA\\Mail\\Service\\Sync\\ImapToDbSynchronizer",
        "type": "->",
        "args": [
          "*** sensitive parameters replaced ***"
        ]
      },
      {
        "file": "/var/www/nextcloud/apps/mail/lib/BackgroundJob/SyncJob.php",
        "line": 93,
        "function": "syncAccount",
        "class": "OCA\\Mail\\Service\\Sync\\ImapToDbSynchronizer",
        "type": "->",
        "args": [
          "*** sensitive parameters replaced ***"
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/public/BackgroundJob/Job.php",
        "line": 61,
        "function": "run",
        "class": "OCA\\Mail\\BackgroundJob\\SyncJob",
        "type": "->"
      },
      {
        "file": "/var/www/nextcloud/lib/public/BackgroundJob/TimedJob.php",
        "line": 88,
        "function": "start",
        "class": "OCP\\BackgroundJob\\Job",
        "type": "->"
      },
      {
        "file": "/var/www/nextcloud/lib/public/BackgroundJob/TimedJob.php",
        "line": 75,
        "function": "start",
        "class": "OCP\\BackgroundJob\\TimedJob",
        "type": "->"
      },
      {
        "file": "/var/www/nextcloud/cron.php",
        "line": 162,
        "function": "execute",
        "class": "OCP\\BackgroundJob\\TimedJob",
        "type": "->"
      }
    ],
    "File": "/var/www/nextcloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php",
    "Line": 282,
    "Previous": {
      "Exception": "Error",
      "Message": "Call to a member function getUid() on null",
      "Code": 0,
      "Trace": [
        {
          "file": "/var/www/nextcloud/apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Socket.php",
          "line": 1236,
          "function": "_sendCmd",
          "class": "Horde_Imap_Client_Socket",
          "type": "->"
        },
        {
          "file": "/var/www/nextcloud/apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Base.php",
          "line": 1066,
          "function": "_openMailbox",
          "class": "Horde_Imap_Client_Socket",
          "type": "->"
        },
        {
          "file": "/var/www/nextcloud/apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Base.php",
          "line": 1694,
          "function": "openMailbox",
          "class": "Horde_Imap_Client_Base",
          "type": "->"
        },
        {
          "file": "/var/www/nextcloud/apps/mail/lib/Service/MailManager.php",
          "line": 802,
          "function": "status",
          "class": "Horde_Imap_Client_Base",
          "type": "->"
        },
        {
          "file": "/var/www/nextcloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php",
          "line": 479,
          "function": "isPermflagsEnabled",
          "class": "OCA\\Mail\\Service\\MailManager",
          "type": "->"
        },
        {
          "file": "/var/www/nextcloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php",
          "line": 263,
          "function": "runPartialSync",
          "class": "OCA\\Mail\\Service\\Sync\\ImapToDbSynchronizer",
          "type": "->"
        },
        {
          "file": "/var/www/nextcloud/apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php",
          "line": 133,
          "function": "sync",
          "class": "OCA\\Mail\\Service\\Sync\\ImapToDbSynchronizer",
          "type": "->",
          "args": [
            "*** sensitive parameters replaced ***"
          ]
        },
        {
          "file": "/var/www/nextcloud/apps/mail/lib/BackgroundJob/SyncJob.php",
          "line": 93,
          "function": "syncAccount",
          "class": "OCA\\Mail\\Service\\Sync\\ImapToDbSynchronizer",
          "type": "->",
          "args": [
            "*** sensitive parameters replaced ***"
          ]
        },
        {
          "file": "/var/www/nextcloud/lib/public/BackgroundJob/Job.php",
          "line": 61,
          "function": "run",
          "class": "OCA\\Mail\\BackgroundJob\\SyncJob",
          "type": "->"
        },
        {
          "file": "/var/www/nextcloud/lib/public/BackgroundJob/TimedJob.php",
          "line": 88,
          "function": "start",
          "class": "OCP\\BackgroundJob\\Job",
          "type": "->"
        },
        {
          "file": "/var/www/nextcloud/lib/public/BackgroundJob/TimedJob.php",
          "line": 75,
          "function": "start",
          "class": "OCP\\BackgroundJob\\TimedJob",
          "type": "->"
        },
        {
          "file": "/var/www/nextcloud/cron.php",
          "line": 162,
          "function": "execute",
          "class": "OCP\\BackgroundJob\\TimedJob",
          "type": "->"
        }
      ],
      "File": "/var/www/nextcloud/apps/mail/vendor/bytestream/horde-imap-client/lib/Horde/Imap/Client/Socket.php",
      "Line": 4248
    },
    "message": "Cron mail sync failed for account {accountId}",
    "exception": [],
    "CustomMessage": "Cron mail sync failed for account 35"
  },
  "id": "6841435c6d602"
}

Start with apps/mail/lib/Service/Sync/ImapToDbSynchronizer.php, especially lines 133, 263, 282, and 479, and follow the stack trace through MailManager.php and BackgroundJob/SyncJob.php. Reproduce the cron sync failure and trace why getUid() is called on null. Done means the affected account can complete cron mail synchronization without this error.