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);
    }

            // 404
            throw responseManager.new404("Thumbnail for " + form.docId + " is not found.");
        }

        final File thumbnailFile = thumbnailManager.getThumbnailFile(doc);
        if (thumbnailFile == null) {
            if (fessConfig.isThumbnailEnabled()) {
                thumbnailManager.offer(doc);
            }
            // 404