Registering user against custom database connection with auto-migration doesn't work

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Hi, i follow along this tutorial Connecting Auth0 to MongoDB with Custom Databases.

it’s ok for login. but when signup it’s always says that:
We’re sorry, something went wrong when attempting to sign up.

actually user registered successfully, bot still stuck at signup form.

9:42:40 PM:
 Connected
9:50:06 PM:
 new webtask request
9:50:07 PM:
 finished webtask request
9:50:07 PM:
 new webtask request
9:50:08 PM:
 finished webtask request
9:50:08 PM:
 new webtask request
9:50:08 PM:
 {
  "code": 400,
  "message": "Compilation failed: Unexpected token }",
  "error": "Unexpected token }",
  "stack": "/data/io/node8/440c0a10-7e02-4883-bbb5-f57bc438d9da/webtask.js:7\n}\n^\n\nSyntaxError: Unexpected token }\n    at createScript (vm.js:80:10)\n    at Object.runInThisContext (vm.js:139:10)\n    at WebtaskModule.compileWebtask (/data/sandbox/lib/module.js:157:30)\n    at defaultJavascriptCompiler (/data/sandbox/lib/compiler.js:135:24)\n    at defaultCompiler (/data/sandbox/lib/compiler.js:144:12)\n    at /data/sandbox/lib/compiler.js:276:11\n    at /data/sandbox/node8/node_modules/async/dist/async.js:3880:24\n    at replenish (/data/sandbox/node8/node_modules/async/dist/async.js:1011:17)\n    at /data/sandbox/node8/node_modules/async/dist/async.js:1016:9\n    at eachOfLimit (/data/sandbox/node8/node_modules/async/dist/async.js:1041:24)"
}
9:50:08 PM:
 finished webtask request
9:50:30 PM:
 new webtask request
9:50:31 PM:
 finished webtask request
9:50:31 PM:
 new webtask request
9:50:31 PM:
 finished webtask request
9:50:31 PM:
 new webtask request
9:50:32 PM:
 finished webtask request
9:50:32 PM:
 new webtask request
9:50:33 PM:
 finished webtask request