docMap.put("url", "http://example.com");

        boolean result = thumbnailManager.offer(docMap);
        assertFalse(result);
    }

    // Test offer with null task
    public void test_offer_nullTask() {
        TestThumbnailGenerator generator = new TestThumbnailGenerator();
        generator.available = true;
        generator.target = true;
        generator.task = null;