aws-cdk-lib/aws-ssm: StringListParameter (Error in FnJoin)

### Describe the bug

I added a StringListParameter to my existing Stack and suddenly get the following error:

```
Error: FnJoin requires at least one value to be provided
at Function.join (/Users/path_to_my_git_repo/node_modules/aws-cdk-lib/core/lib/cfn-fn.js:1:1026)
at new StringListParameter (/Users/path_to_my_git_repo/node_modules/aws-cdk-lib/aws-ssm/lib/parameter.js:1:13016)
at EosAwsAccountMlBootstrapStack.setupVpc (/Users/path_to_my_git_repo/lib/eos-aws-account-ml-bootstrap-stack.ts:157:5)
at new EosAwsAccountMlBootstrapStack (/Users/path_to_my_git_repo/lib/eos-aws-account-ml-bootstrap-stack.ts:42:10)
at Object. (/Users/path_to_my_git_repo/bin/eos-aws-account-ml-bootstrap.ts:29:1)
at Module._compile (node:internal/modules/cjs/loader:1256:14)
at Module.m._compile (/Users/path_to_my_git_repo/node_modules/ts-node/src/index.ts:1618:23)
at Module._extensions..js (node:internal/modules/cjs/loader:1310:10)
at Object.require.extensions. [as .ts] (/Users/path_to_my_git_repo/node_modules/ts-node/src/index.ts:1621:12)
at Module.load (node:internal/modules/cjs/loader:1119:32)
```

Here is the code I added:

```
const vpc = ec2.Vpc.fromLookup(this, "Vpc", {
vpcName: vpcName,
subnetGroupNameTag: "type",
})

const appSubnetGroupSelections = vpc.selectSubnets({
subnetGroupName: "app",
})

new cdk.aws_ssm.StringListParameter(this, "VpcParamSubnets", {
parameterName: "/iac/vpc/appSubnetIds",
stringListValue: appSubnetGroupSelections.subnetIds,
})
```

### Expected Behavior

Successfully synth and deploy stack.

### Current Behavior

Cannot synth or deploy stack.

### Reproduction Steps

For some reason this error only occurs in some AWS accounts but not in others so it may be hard to reproduce. We roll out this stack in 8 different accounts and I currently cannot tell why it fails in one account but not the others.

### Possible Solution

_No response_

### Additional Information/Context

_No response_

### CDK CLI Version

2.103.1

### Framework Version

_No response_

### Node.js Version

v18.17.0

### OS

MacOS Sonoma 14.1

### Language

TypeScript

### Language Version

_No response_

### Other information

_No response_

Start with aws-ssm/lib/parameter.js at the StringListParameter stack-trace location, then compare it with the caller in lib/eos-aws-account-ml-bootstrap-stack.ts:157 and the VPC subnet selection shown in the report. Reproduce the synth in an affected account and compare the selected subnet IDs with a working account; done means the reported configuration synthesizes successfully without the FnJoin error.

Written by the indexing model from the issue text.