Error when searching for files in dashboard

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I'm seeing this error message when doing an "advanced search" in the file manager. I search for a custom field.

Call to a member function getTreeNodePermissionsNodeID() on null
Details
/home/public/sites/<site>/concrete/src/Permission/Assignment/FileAssignment.php(68): Error->null   
/home/public/sites/<site>/concrete/src/Permission/Key/Key.php(474): Concrete\Core\Permission\Assignment\FileAssignment->getPermissionAccessObject   
/home/public/sites/<site>/concrete/src/Permission/Key/FileKey.php(18): Concrete\Core\Permission\Key\Key->getPermissionAccessObject   
/home/public/sites/<site>/concrete/src/Permission/Response/Response.php(109): Concrete\Core\Permission\Key\FileKey->validate   
/home/public/sites/<site>/concrete/src/Permission/Response/Response.php(109): null->call_user_func_array   
/home/public/sites/<site>/concrete/src/Permission/Response/Response.php(119): Concrete\Core\Permission\Response\Response->validate   
/home/public/sites/<site>/concrete/src/Permission/Checker.php(75): Concrete\Core\Permission\Response\Response->__call   
/home/public/sites/<site>/concrete/src/Entity/File/Version.php(1772): Concrete\Core\Permission\Checker->__call   
/home/public/sites/<site>/concrete/src/Entity/File/File.php(109): Concrete\Core\Entity\File\Version->getJSONObject   
/home/public/sites/<site>/concrete/src/Entity/File/File.php(109): null->call_user_func_array   
/home/public/sites/<site>/concrete/src/File/Search/Result/Item.php(23): Concrete\Core\Entity\File\File->__call   
/home/public/sites/<site>/concrete/src/File/Search/Result/Item.php(15): Concrete\Core\File\Search\Result\Item->populateDetails   
/home/public/sites/<site>/concrete/src/File/Search/Result/Result.php(98): Concrete\Core\File\Search\Result\Item->__construct


PHP version 7.1.25-1+0~20181207224650.11+stretch~1.gbpf65b84
Concrete5 version:
Core Version - 8.4.3
Version Installed - 8.4.3
Database Version - 20180716000000

Any ideas on how to fix this issue?