For our API integration when calling this endpoint GET `/files/{file_id}` the return value for modified_by occasionally returns empty strings for the “name” and “login” fields. Example:

 

{
    "type": "file",
    "id": "<file_id>",
    "name": "Outline.doc",
    "parent": {"type": "folder", "id": "<folder_id>", "name": "My Documents"},
    "extension": "doc",
    "size": 20480,
    "sha1": "<hash>",
    "item_status": "active",
    "owned_by": {"type": "user", "id": "<user_id_1>", "name": "<name>", "login": "<email>"},
    "created_by": {"type": "user", "id": "<user_id_2>", "name": "", "login": ""},
    "modified_by": {"type": "user", "id": "<user_id_2>", "name": "", "login": ""},
}

when following up on this call and querying the user_id with GET `/users/{user_id}` the API is returning a 404 not found status.

What is this mystery user? Am I doing something wrong in my calls that might be causing this? The call is correctly using the `as-user` header when needed, and has these fields separated by commas in the params: 

FILE_FIELDS = _'id', 'parent', 'name', 'extension', 'size', 'sha1', 'item_status', 'created_by', 'owned_by',

'modified_by', 'path_collection', 'shared_link', 'has_collaborations', 'created_at', 'modified_at',

'has_collaborations']

Thank you for any assistance here.