regression: app reports unknown-account/unknown-region to toolkit if stack doesn't have explicit env

[eladb]

The current (unreleased) version of the CDK (in master) has a regression caused by #2728, where the app reports this environment: aws://unknown-account/unknown-region to the cli.

[coderbyheart]

I see this issue still in 1.2.0. I run CDK in CodeBuild and it complains about the CDKToolkit stack not found (but it exists):

[Container] 2019/07/31 07:11:19 Running command npx cdk deploy --trace -v --require-approval never '*' 
CDK toolkit version: 1.2.0 (build 6b763b7) 
Command line arguments: { _: [ 'deploy' ], 
  'ignore-errors': false, 
  ignoreErrors: false, 
  json: false, 
  j: false, 
  verbose: true, 
  v: true, 
  ec2creds: undefined, 
  i: undefined, 
  'version-reporting': undefined, 
  versionReporting: undefined, 
  'path-metadata': true, 
  pathMetadata: true, 
  'asset-metadata': true, 
  assetMetadata: true, 
  staging: true, 
  ci: false, 
  trace: true, 
  'require-approval': 'never', 
  requireApproval: 'never', 
  'role-arn': undefined, 
  r: undefined, 
  roleArn: undefined, 
  'build-exclude': [], 
  E: [], 
  buildExclude: [], 
  '$0': 'node_modules/.bin/cdk', 
  STACKS: [ '*' ], 
  stacks: [ '*' ] } 
cdk.json: { 
  "app": "node dist/cdk/cloudformation.js" 
} 
merged settings: { versionReporting: true, 
  pathMetadata: true, 
  output: 'cdk.out', 
  app: 'node dist/cdk/cloudformation.js', 
  context: {}, 
  tags: [], 
  assetMetadata: true, 
  requireApproval: 'never', 
  staging: true } 
Setting "CDK_DEFAULT_REGION" environment variable to eu-central-1 
Resolving default credentials 
Looking up default account ID from STS 
Default account ID: 77XXXXXXXX 
Setting "CDK_DEFAULT_ACCOUNT" environment variable to 77XXXXXXXX 
context: { 'aws:cdk:enable-path-metadata': true, 
  'aws:cdk:enable-asset-metadata': true } 
outdir: cdk.out 
env: { CDK_DEFAULT_REGION: 'eu-central-1', 
  CDK_DEFAULT_ACCOUNT: '77XXXXXXXX', 
  CDK_CONTEXT_JSON: 
   '{"aws:cdk:enable-path-metadata":true,"aws:cdk:enable-asset-metadata":true}', 
  CDK_OUTDIR: 'cdk.out' } 
bifravst: deploying... 
Using default AWS SDK credentials for account 77XXXXXXXX 
Waiting for stack CDKToolkit to finish creating or updating... 
Stack CDKToolkit does not exist 
The environment aws://unknown-account/unknown-region doesn't have the CDK toolkit stack (CDKToolkit) installed. Use cdk bootstrap "aws://unknown-account/unknown-region" to setup your environment for use with the toolkit. 
Using default AWS SDK credentials for account 77XXXXXXXX 
Attempting to create ChangeSet CDK-fd4ead4f-3271-4059-b941-eb8d9d39f956 to update stack bifravst 
bifravst: creating CloudFormation changeset...