hexo: Misleading Nunjucks error message

Check List

Please check followings before submitting a new issue.

• I have already read Docs page & Troubleshooting page
• I have already searched existing issues and they are not help to me
• I examined error or warning messages and it’s difficult to solve
• Using the latest version of Hexo (run hexo version to check)
• Node.js is higher than 8.6.0

Question

Error message below is shown (I’m sure that I have filled in url: field in my hexo _config.yml)

[myname@myname-pc blog_src]$ hexo g
INFO  Start processing
INFO  Files loaded in 378 ms
ERROR Render HTML failed: about/index.html
TypeError: Cannot read property 'replace' of null
    at Hexo.externalLinkFilter (/home/myname/Projects/blog_src/node_modules/hexo/lib/plugins/filter/after_render/external_link.js:45:15)                                                                                                                               
    at Hexo.tryCatcher (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/util.js:16:23)
    at Hexo.<anonymous> (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/method.js:15:34)
    at /home/myname/Projects/blog_src/node_modules/hexo/lib/extend/filter.js:60:50
    at tryCatcher (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/util.js:16:23)
    at Object.gotValue (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/reduce.js:166:18)
    at Object.gotAccum (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/reduce.js:155:25)
    at Object.tryCatcher (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/util.js:16:23)
    at Promise._settlePromiseFromHandler (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/promise.js:547:31)
    at Promise._settlePromise (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/promise.js:604:18)
    at Promise._settlePromiseCtx (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/promise.js:641:10)
    at _drainQueueStep (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/async.js:97:12)
    at _drainQueue (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/async.js:86:9)
    at Async._drainQueues (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/async.js:102:5)
    at Immediate.Async.drainQueues [as _onImmediate] (/home/myname/Projects/blog_src/node_modules/bluebird/js/release/async.js:15:14)                                                                                                                                  
    at processImmediate (internal/timers.js:439:21)

Environment & Settings

Node.js & npm version

hexo: 4.0.0
hexo-cli: 3.1.0
os: Linux 5.3.8-3-MANJARO linux x64
node: 13.1.0
v8: 7.8.279.17-node.19
uv: 1.33.1
zlib: 1.2.11
brotli: 1.0.7
ares: 1.15.0
modules: 79
nghttp2: 1.39.2
napi: 5
llhttp: 1.1.4
openssl: 1.1.1d
cldr: 35.1
icu: 64.2
tz: 2019a
unicode: 12.1

Your site _config.yml (Optional)

Your theme _config.yml (Optional)

Hexo and Plugin version(npm ls --depth 0)

hexo-site@0.0.0 /home/txshi/Projects/blog_src
├── hexo@4.0.0
├── hexo-generator-archive@1.0.0
├── hexo-generator-category@1.0.0
├── hexo-generator-index@1.0.0
├── hexo-generator-tag@1.0.0
├── hexo-renderer-ejs@1.0.0
├── hexo-renderer-marked@2.0.0
├── hexo-renderer-stylus@1.1.0
└── hexo-server@1.0.0

Your package.json package.json

{
  "name": "hexo-site",
  "version": "0.0.0",
  "private": true,
  "scripts": {
    "build": "hexo generate",
    "clean": "hexo clean",
    "deploy": "hexo deploy",
    "server": "hexo server"
  },
  "hexo": {
    "version": "4.0.0"
  },
  "dependencies": {
    "hexo": "^4.0.0",
    "hexo-generator-archive": "^1.0.0",
    "hexo-generator-category": "^1.0.0",
    "hexo-generator-index": "^1.0.0",
    "hexo-generator-tag": "^1.0.0",
    "hexo-renderer-ejs": "^1.0.0",
    "hexo-renderer-stylus": "^1.1.0",
    "hexo-renderer-marked": "^2.0.0",
    "hexo-server": "^1.0.0"
  }
}

Others