[transfer] Can't create user separately from Server?

I have an existing Transfer instance. I would like to automatically create users for it via cdk at later times as needed.

Reproduction Steps

def make_user(user_name, server_id, ssh_public_key):

    app = core.App()
    UserStack(scope=app,
              id='sftp-transfer-user-' + user_name,
              description='SFTP Transfer User for ' + user_name,
              settings=settings,
              env=env,
              user_name=user_name,
              server_id=server_id,
              ssh_public_key=ssh_public_key)
    app.synth()

class UserStack(core.Stack):

    def __init__(self, scope: core.Construct, id: str,
                 settings: Settings, **kwargs) -> None:

        super().__init__(scope, id)
        env = settings.get_environment()

        CfnUser(scope,
                id=f"sftp-user-{kwargs['user_name']}",
                role=settings.get_role_arn(),
                server_id=kwargs['server_id'],
                user_name=kwargs['user_name'],
                home_directory_type="LOGICAL",
                home_directory_mappings=[self.MEP("/in", "/sftp-bucket/${Transfer:UserName}/in"),
                                         self.MEP("/out", "/sftp-bucket/${Transfer:UserName}/out"),
                                         self.MEP("/", "/sftp-bucket/${Transfer:UserName}")],
                ssh_public_keys=[kwargs['ssh_public_key']])


    def MEP(self, entry, target):
        return aws_transfer.CfnUser.HomeDirectoryMapEntryProperty(entry=entry, target=target)

Error mesage is:

jsii.errors.JavaScriptError: 
  Error: CfnUser at 'sftp-user-foo-test' should be created in the scope of a Stack, but no Stack found
      at _lookup (/private/var/folders/kf/031yw5wx3hnfj7by8xsjz4jc0000gn/T/jsii-kernel-Ari9yh/node_modules/@aws-cdk/core/lib/stack.js:137:23)
      at _lookup (/private/var/folders/kf/031yw5wx3hnfj7by8xsjz4jc0000gn/T/jsii-kernel-Ari9yh/node_modules/@aws-cdk/core/lib/stack.js:139:20)
      at Function.of (/private/var/folders/kf/031yw5wx3hnfj7by8xsjz4jc0000gn/T/jsii-kernel-Ari9yh/node_modules/@aws-cdk/core/lib/stack.js:121:27)
      at new CfnElement (/private/var/folders/kf/031yw5wx3hnfj7by8xsjz4jc0000gn/T/jsii-kernel-Ari9yh/node_modules/@aws-cdk/core/lib/cfn-element.js:25:36)
      at new CfnRefElement (/private/var/folders/kf/031yw5wx3hnfj7by8xsjz4jc0000gn/T/jsii-kernel-Ari9yh/node_modules/@aws-cdk/core/lib/cfn-element.js:98:1)
      at new CfnResource (/private/var/folders/kf/031yw5wx3hnfj7by8xsjz4jc0000gn/T/jsii-kernel-Ari9yh/node_modules/@aws-cdk/core/lib/cfn-resource.js:23:9)
      at new CfnUser (/private/var/folders/kf/031yw5wx3hnfj7by8xsjz4jc0000gn/T/jsii-kernel-Ari9yh/node_modules/@aws-cdk/aws-transfer/lib/transfer.generated.js:340:9)
      at /Users/joel/PycharmProjects/venvs/sftp/lib/python3.8/site-packages/jsii/_embedded/jsii/jsii-runtime.js:3137:49
      at Kernel._wrapSandboxCode (/Users/joel/PycharmProjects/venvs/sftp/lib/python3.8/site-packages/jsii/_embedded/jsii/jsii-runtime.js:3621:16)
      at Kernel._create (/Users/joel/PycharmProjects/venvs/sftp/lib/python3.8/site-packages/jsii/_embedded/jsii/jsii-runtime.js:3137:26)

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "transfer_app.py", line 52, in <module>
    make_user(cust_name, server_id, ssh_pub_key)
  File "transfer_app.py", line 30, in make_user
    UserStack(scope=app,
  File "/Users/joel/PycharmProjects/venvs/sftp/lib/python3.8/site-packages/jsii/_runtime.py", line 69, in __call__
    inst = super().__call__(*args, **kwargs)
  File "/Users/joel/PycharmProjects/shift-ux-backend/.cfn/stacks/transfer_stack.py", line 28, in __init__
    CfnUser(scope,
  File "/Users/joel/PycharmProjects/venvs/sftp/lib/python3.8/site-packages/jsii/_runtime.py", line 69, in __call__
    inst = super().__call__(*args, **kwargs)
  File "/Users/joel/PycharmProjects/venvs/sftp/lib/python3.8/site-packages/aws_cdk/aws_transfer/__init__.py", line 608, in __init__
    jsii.create(CfnUser, self, [scope, id, props])
  File "/Users/joel/PycharmProjects/venvs/sftp/lib/python3.8/site-packages/jsii/_kernel/__init__.py", line 250, in create
    response = self.provider.create(
  File "/Users/joel/PycharmProjects/venvs/sftp/lib/python3.8/site-packages/jsii/_kernel/providers/process.py", line 347, in create
    return self._process.send(request, CreateResponse)
  File "/Users/joel/PycharmProjects/venvs/sftp/lib/python3.8/site-packages/jsii/_kernel/providers/process.py", line 332, in send
    raise JSIIError(resp.error) from JavaScriptError(resp.stack)
jsii.errors.JSIIError: CfnUser at 'sftp-user-foo-test' should be created in the scope of a Stack, but no Stack found

What did you expect to happen?

I expected an SFTP user to be created on the given server_id.

What actually happened?

Stack cannot be found?

jsii.errors.JSIIError: CfnUser at 'sftp-user-foo-test' should be created in the scope of a Stack, but no Stack found

Environment

• CLI Version : aws-cli/1.18.148 Python/3.5.3 Darwin/19.6.0 botocore/1.18.7
• Framework Version:
• Node.js Version: v15.01
• OS : Darwin, OSX
• Language (Version): Python 3.5.3

Other

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This is 🐛 Bug Report

[jbremson]

User error.

[mimozell]

@kiturutin I added a similar issue with the fix here. Hope it helps! I can elaborate further if needed.