Map<String, Object> docMap = new HashMap<>();
        docMap.put("mimetype", "application/unknown");
        assertFalse(thumbnailGenerator.isTarget(docMap));
    }

    @Test
    public void test_isTarget_withNullDocMap() {
        // Test with null document map
        assertFalse(thumbnailGenerator.isTarget(null));
    }

    @Test
    public void test_isTarget_withEmptyDocMap() {