File result = thumbnailManager.getThumbnailFile(docMap);
        assertNull(result);
    }

    // Test getThumbnailFile with blank path
    @Test
    public void test_getThumbnailFile_blankPath() {
        Map<String, Object> docMap = new HashMap<>();
        // No _id field, so docid will be null

        File result = thumbnailManager.getThumbnailFile(docMap);
        assertNull(result);