cdk deploy fails due to stack using assets

Following along the README I tried to deploy the template to an AWS-account after using

`cdk bootstrap aws://my_id/us_east_2`

which ended up in
```
⏳ Bootstrapping environment aws://my_id/us-east-2...
✅ Environment aws://my_id/us-east-2 bootstrapped (no changes).
```

but the `cdk deploy` ended up like this

```
❯ cdk deploy
❌ lambdaapp failed: Error: This stack uses assets, so the toolkit stack must be deployed to the environment (Run "cdk bootstrap aws://unknown-account/unknown-region")
at Object.addMetadataAssetsToManifest (/home/mhi/.nvm/versions/node/v14.16.0/lib/node_modules/aws-cdk/lib/assets.ts:27:11)
at Object.deployStack (/home/mhi/.nvm/versions/node/v14.16.0/lib/node_modules/aws-cdk/lib/api/deploy-stack.ts:211:29)
at processTicksAndRejections (internal/process/task_queues.js:93:5)
at CdkToolkit.deploy (/home/mhi/.nvm/versions/node/v14.16.0/lib/node_modules/aws-cdk/lib/cdk-toolkit.ts:180:24)
at initCommandLine (/home/mhi/.nvm/versions/node/v14.16.0/lib/node_modules/aws-cdk/bin/cdk.ts:208:9)
This stack uses assets, so the toolkit stack must be deployed to the environment (Run "cdk bootstrap aws://unknown-account/unknown-region")
```

Is that due to a wrong region that was chosen? The AWS Account ID I took from the `My Security Credentials` section in the AWS Management Console.

Start with the README instructions and compare the account and region used by `cdk bootstrap aws://my_id/us_east_2` with the environment resolved by `cdk deploy`. Reproduce the failure and determine why the deploy reports `unknown-account/unknown-region`; done means the documented deployment completes without the assets/bootstrap error.

索引モデルが issue の本文から書いたものです。