Fail to run the `appengine/static-files` sample

[steren]

$ npm i
[...]
$ npm start
Error: `line` is not an integer
    at Parser.initBlock (/Users/steren/work/nodejs-docs-samples/appengine/static-files/node_modules/pug-parser/index.js:156:36)
    at Parser.emptyBlock (/Users/steren/work/nodejs-docs-samples/appengine/static-files/node_modules/pug-parser/index.js:168:17)
    at Parser.parseTag (/Users/steren/work/nodejs-docs-samples/appengine/static-files/node_modules/pug-parser/index.js:1040:19)
    at Parser.parseExpr (/Users/steren/work/nodejs-docs-samples/appengine/static-files/node_modules/pug-parser/index.js:208:21)
    at Parser.parse (/Users/steren/work/nodejs-docs-samples/appengine/static-files/node_modules/pug-parser/index.js:112:25)
    at parse (/Users/steren/work/nodejs-docs-samples/appengine/static-files/node_modules/pug-parser/index.js:12:20)
    at Object.parse (/Users/steren/work/nodejs-docs-samples/appengine/static-files/node_modules/pug/lib/index.js:125:22)
    at Function.loadString [as string] (/Users/steren/work/nodejs-docs-samples/appengine/static-files/node_modules/pug-load/index.js:45:21)
    at compileBody (/Users/steren/work/nodejs-docs-samples/appengine/static-files/node_modules/pug/lib/index.js:86:18)
    at Object.exports.compile (/Users/steren/work/nodejs-docs-samples/appengine/static-files/node_modules/pug/lib/index.js:242:16)