Trying to access array offset on value of type null at /lib/FilesHooks.php#471

Nextcloud 24.0.9.

{
  "reqId": "Ln4zf0y4OwEBrrxQBull",
  "level": 3,
  "time": "2023-01-20T07:59:14+00:00",
  "remoteAddr": "77.21.8.20",
  "user": "laris",
  "app": "PHP",
  "method": "MOVE",
  "url": "/remote.php/dav/files/laris/FOLDER%201/FOLDER%202",
  "message": "Trying to access array offset on value of type null at /var/www/nextcloud/apps/activity/lib/FilesHooks.php#471",
  "userAgent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/109.0.0.0 Safari/537.36",
  "version": "24.0.9.2",
  "exception": {
    "Exception": "Error",
    "Message": "Trying to access array offset on value of type null at /var/www/nextcloud/apps/activity/lib/FilesHooks.php#471",
    "Code": 0,
    "Trace": [
      {
        "file": "/var/www/nextcloud/apps/activity/lib/FilesHooks.php",
        "line": 471,
        "function": "onError",
        "class": "OC\\Log\\ErrorHandler",
        "type": "::",
        "args": [
          2,
          "Trying to access array offset on value of type null",
          "/var/www/nextcloud/apps/activity/lib/FilesHooks.php",
          471
        ]
      },
      {
        "file": "/var/www/nextcloud/apps/activity/lib/FilesHooks.php",
        "line": 386,
        "function": "fileMoving",
        "class": "OCA\\Activity\\FilesHooks",
        "type": "->",
        "args": [
          "/FOLDER 1/FOLDER 2",
          "/FOLDER 1/FOLDER 3/FOLDER 4"
        ]
      },
      {
        "file": "/var/www/nextcloud/apps/activity/lib/FilesHooksStatic.php",
        "line": 79,
        "function": "fileMovePost",
        "class": "OCA\\Activity\\FilesHooks",
        "type": "->",
        "args": [
          "/FOLDER 1/FOLDER 2",
          "/FOLDER 1/FOLDER 3/FOLDER 4"
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/private/legacy/OC_Hook.php",
        "line": 106,
        "function": "fileMovePost",
        "class": "OCA\\Activity\\FilesHooksStatic",
        "type": "::",
        "args": [
          [
            "/FOLDER 1/FOLDER 2",
            "/FOLDER 1/FOLDER 3/FOLDER 4"
          ]
        ]
      },
      {
        "file": "/var/www/nextcloud/lib/private/Files/View.php",
        "line": 866,
        "function": "emit",
        "class": "OC_Hook",
        "type": "::",
        "args": [
          "OC_Filesystem",
          "post_rename",
          [
            "/FOLDER 1/FOLDER 2",
            "/FOLDER 1/FOLDER 3/FOLDER 4"
          ]
        ]
      },
      {
        "file": "/var/www/nextcloud/apps/dav/lib/Connector/Sabre/Directory.php",
        "line": 455,
        "function": "rename",
        "class": "OC\\Files\\View",
        "type": "->",
        "args": [
          "/FOLDER 1/FOLDER 2",
          "/FOLDER 1/FOLDER 3/FOLDER 4"
        ]
      },
      {
        "file": "/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Tree.php",
        "line": 160,
        "function": "moveInto",
        "class": "OCA\\DAV\\Connector\\Sabre\\Directory",
        "type": "->",
        "args": [
          "1 - DOCUMENTS ADMINISTRATIFS",
          "files/laris/FOLDER 1/FOLDER 2",
          {
            "__class__": "OCA\\DAV\\Connector\\Sabre\\Directory"
          }
        ]
      },
      {
        "file": "/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/CorePlugin.php",
        "line": 612,
        "function": "move",
        "class": "Sabre\\DAV\\Tree",
        "type": "->",
        "args": [
          "files/laris/FOLDER 1/FOLDER 2",
          "files/laris/FOLDER 1/FOLDER 3/FOLDER 4"
        ]
      },
      {
        "file": "/var/www/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php",
        "line": 89,
        "function": "httpMove",
        "class": "Sabre\\DAV\\CorePlugin",
        "type": "->",
        "args": [
          {
            "__class__": "Sabre\\HTTP\\Request"
          },
          {
            "__class__": "Sabre\\HTTP\\Response"
          }
        ]
      },
      {
        "file": "/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php",
        "line": 472,
        "function": "emit",
        "class": "Sabre\\DAV\\Server",
        "type": "->",
        "args": [
          "method:MOVE",
          [
            {
              "__class__": "Sabre\\HTTP\\Request"
            },
            {
              "__class__": "Sabre\\HTTP\\Response"
            }
          ]
        ]
      },
      {
        "file": "/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php",
        "line": 253,
        "function": "invokeMethod",
        "class": "Sabre\\DAV\\Server",
        "type": "->",
        "args": [
          {
            "__class__": "Sabre\\HTTP\\Request"
          },
          {
            "__class__": "Sabre\\HTTP\\Response"
          }
        ]
      },
      {
        "file": "/var/www/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php",
        "line": 321,
        "function": "start",
        "class": "Sabre\\DAV\\Server",
        "type": "->",
        "args": []
      },
      {
        "file": "/var/www/nextcloud/apps/dav/lib/Server.php",
        "line": 358,
        "function": "exec",
        "class": "Sabre\\DAV\\Server",
        "type": "->",
        "args": []
      },
      {
        "file": "/var/www/nextcloud/apps/dav/appinfo/v2/remote.php",
        "line": 35,
        "function": "exec",
        "class": "OCA\\DAV\\Server",
        "type": "->",
        "args": []
      },
      {
        "file": "/var/www/nextcloud/remote.php",
        "line": 170,
        "args": [
          "/var/www/nextcloud/apps/dav/appinfo/v2/remote.php"
        ],
        "function": "require_once"
      }
    ],
    "File": "/var/www/nextcloud/lib/private/Log/ErrorHandler.php",
    "Line": 92,
    "CustomMessage": "--"
  },
  "id": "63ca86e66b7ca"
}

Start with apps/activity/lib/FilesHooks.php at line 471 and trace the fileMoving call from line 386, using the MOVE paths in the report as context. Check how the null value reaches the array offset, then verify that the reported move no longer produces the PHP error.