null values are not allowed in templates when ResultPath=JsonPath.DISCARD

[ck-on-github]

Describe the bug

I am using the Python CDK to generate a CloudFormation template in json format.

cdk deploy of the json CloudFormation template generated using the code snippet:

StepFunctionsStartExecution(
    ...
    result_path=JsonPath.DISCARD
    ...
)

fails with

[/Resources/CfTemplate747CB3D5/Type/DefinitionString/Fn::Join/1/33] 'null' values are not allowed in templates

on aws-cdk-lib=2.70.0

Expected Behavior

Before aws-cdk-lib=2.70.0, the ResultPath in the json template looks like:

\"ResultPath\": null,

and CDK deploy succeeds.

Current Behavior

After aws-cdk-lib=2.70.0, the ResultPath in the json template looks like:

\"ResultPath\": \"",
       null, 
 "\",

and CDK deploy fails with 'null' values are not allowed in templates.

Reproduction Steps

CDK version 2.70.0 or higher.

Possible Solution

No response

Additional Information/Context

No response

CDK CLI Version

2.70.0

Framework Version

No response

Node.js Version

18.18.2

OS

Linux

Language

Python

Language Version

3.8.17

Other information

No response

[pahud]

Can you share a minimal full sample of your code that we can run in our environment? It's probably related to #28661 but we need more details about it.

[ck-on-github]

this was due to converting the StateGraph instance to json with json.dumps instead of using Stack.to_json_string.

[github-actions]

⚠️COMMENT VISIBILITY WARNING⚠️

Comments on closed issues are hard for our team to see.
If you need more assistance, please either tag a team member or open a new issue that references this one.
If you wish to keep having a conversation with other community members under this issue feel free to do so.