diff --git a/src/config.default.json b/src/config.default.json
index 49777fc..7c9c6b4 100644
--- a/src/config.default.json
+++ b/src/config.default.json
@@ -20,7 +20,7 @@
     "template": "template.ejs",
     "thumbnail_tag": "thumbnail",
     "default_title": "Untitled",
-    "default_thumbnail": null
+    "default_thumbnail": ""
   },
   "rss": {
     "title": "mygitblog RSS feed",
diff --git a/test/config.test.js b/test/config.test.js
index fa72475..74bf82b 100644
--- a/test/config.test.js
+++ b/test/config.test.js
@@ -1,5 +1,6 @@
 /* jshint -W117 */
 const fs = require('fs');
+const path = require('path');
 
 const configFile = 'config.json';
 const tmpConfigFile = 'config.temp.json';
@@ -29,6 +30,18 @@ test('no config', () => {
   expect(config['data_dir']).toBe('data');
 });
 
+test('example config', () => {
+  if (fs.existsSync(configFile))
+    fs.unlinkSync(configFile);
+  fs.copyFileSync(path.join('src', 'config.default.json'), configFile);
+  const data = fs.readFileSync(configFile, {encoding: 'UTF-8'});
+  fs.writeFileSync(configFile, data.replace('3000', '3333'), {encoding: 'UTF-8'});
+  const config = require('../src/config')();
+  expect(config).toBeDefined();
+  expect(config['node_port']).toBe(3333);
+  expect(config['data_dir']).toBe('data');
+});
+
 test('invalid config ignored', () => {
   fs.writeFileSync(configFile, 'invalid JSON');
   const config = require('../src/config')();