(aws-stepfunctions-tasks): TaskInput.fromObject no longer accepts null values

[JohanZackrisson]

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Status:

Overview:

Adding a null value property to jsonPath function under StepFunctionsStartExecution cause error while cdk synth.

TypeError: Cannot convert undefined or null to object

With the support of Jsonata we added additional check for Jsonata variables with function findJsonataExpressions which doesn't handle null values currently causing this issue:

https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/aws-stepfunctions/lib/fields.ts#L525

https://github.com/aws/aws-cdk/blob/main/packages/aws-cdk-lib/aws-stepfunctions/lib/private/jsonata.ts#L3

Affected version >= aws-cdk-lib@2.178.0

Complete Error Message:

"use strict";Object.defineProperty(exports,"__esModule",{value:!0}),exports.findJsonataExpressions=exports.isValidJsonataExpression=void 0;const isValidJsonataExpression=expression=>/^{%(.*)%}$/.test(expression);exports.isValidJsonataExpression=isValidJsonataExpression;const findJsonataExpressions=value=>{const recursive=v=>typeof v=="string"&&(0,exports.isValidJsonataExpression)(v)?[v]:Array.isArray(v)?v.flatMap(recursive):typeof v=="object"?Object.values(v).flatMap(recursive):[];return new Set(recursive(value))};exports.findJsonataExpressions=findJsonataExpressions;
                                                                                                                                                                                                                                                                                                                                                                                                                                                                      ^
TypeError: Cannot convert undefined or null to object
    at Function.values (<anonymous>)
    at recursive (/Users/shikagg/issue_34293/node_modules/aws-cdk-lib/aws-stepfunctions/lib/private/jsonata.js:1:455)

Workaround:

Solution:

Handle the null object in case no jsonata is provided,
PR : https://github.com/aws/aws-cdk/pull/34295/files

Related Issues:

Regression Issue

• Select this option if this issue appears to be a regression.

Last Known Working CDK Version

2.177.0

Expected Behavior

Null values should be accepted

Current Behavior

Synthesis crashes with:

TypeError: Cannot convert undefined or null to object

Reproduction Steps

Create typescript cdk project with the test code:

import * as cdk from 'aws-cdk-lib';
import { Construct } from 'constructs';
import * as sfn from 'aws-cdk-lib/aws-stepfunctions';
import * as tasks from 'aws-cdk-lib/aws-stepfunctions-tasks';

export class CdkBugStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const definition = new sfn.Pass(this, "Test step")

    const stateMachine = new sfn.StateMachine(this, 'Steps', {
      definitionBody: sfn.DefinitionBody.fromChainable(definition),
    });

    const task = new tasks.StepFunctionsStartExecution(this, 'Start migration process', {
      stateMachine: stateMachine,
      integrationPattern: sfn.IntegrationPattern.WAIT_FOR_TASK_TOKEN,
      input: sfn.TaskInput.fromObject({
        token: sfn.JsonPath.taskToken,
        nullProperty: null,
      }),
    });
  }
}

[JohanZackrisson]

It crashes with the stack trace:

    at Function.values (<anonymous>)
    at recursive (/Users/johan.zackrisson/Work/stuff/cdk-bug/node_modules/aws-cdk-lib/aws-stepfunctions/lib/private/jsonata.js:1:455)
    at Array.flatMap (<anonymous>)
    at recursive (/Users/johan.zackrisson/Work/stuff/cdk-bug/node_modules/aws-cdk-lib/aws-stepfunctions/lib/private/jsonata.js:1:465)
    at Array.flatMap (<anonymous>)
    at recursive (/Users/johan.zackrisson/Work/stuff/cdk-bug/node_modules/aws-cdk-lib/aws-stepfunctions/lib/private/jsonata.js:1:465)
    at findJsonataExpressions (/Users/johan.zackrisson/Work/stuff/cdk-bug/node_modules/aws-cdk-lib/aws-stepfunctions/lib/private/jsonata.js:1:502)
    at Function.containsTaskToken (/Users/johan.zackrisson/Work/stuff/cdk-bug/node_modules/aws-cdk-lib/aws-stepfunctions/lib/fields.js:1:7096)
    at new StepFunctionsStartExecution (/Users/johan.zackrisson/Work/stuff/cdk-bug/node_modules/aws-cdk-lib/aws-stepfunctions-tasks/lib/stepfunctions/start-execution.js:1:2014)
    at new CdkBugStack (/Users/johan.zackrisson/Work/stuff/cdk-bug/lib/cdk-bug-stack.ts:16:18)

Which points me to think there is a bug in the containsTaskToken which in turn calls findJsonataExpressions
It looks like findJsonataExpressions doens't handle null values.

[pahud]

Current vs Expected Behavior

graph TD
    subgraph "Current Behavior (v2.178.0+)"
        A["TaskInput.fromObject({ prop: null })"] --> B["StepFunctionsStartExecution._renderTask()"];
        B --> C["Internal _renderParametersOrArguments() called"];
        C --> D{"Handles 'null' value?"};
        D -- No --> E["TypeError: Cannot convert null to object"];
    end

    subgraph "Expected Behavior (v2.177.0)"
        F["TaskInput.fromObject({ prop: null })"] --> G["StepFunctionsStartExecution._renderTask()"];
        G --> H["FieldUtils.renderObject() called"];
        H --> I{"Handles 'null' value?"};
        I -- Yes --> J["'null' value correctly rendered/skipped"];
        J --> K["Synthesis Succeeds"];
    end

Loading

Thanks for reporting this regression and providing clear reproduction steps!

Based on our analysis, the issue stems from a change in how task parameters are rendered internally within the StepFunctionsStartExecution task, introduced in aws-cdk-lib@2.178.0. Previously, the task used a rendering function (FieldUtils.renderObject) that correctly skipped null values in the input object. The newer rendering logic introduced in v2.178.0 appears to attempt processing these null values, leading to the TypeError.

The relevant code change is in the _renderTask method of packages/aws-cdk-lib/aws-stepfunctions-tasks/lib/stepfunctions/start-execution.ts.

aws-cdk/packages/aws-cdk-lib/aws-stepfunctions-tasks/lib/stepfunctions/start-execution.ts

Lines 117 to 143 in 6f0605b

	protected _renderTask(topLevelQueryLanguage?: sfn.QueryLanguage): any {
	const queryLanguage = sfn._getActualQueryLanguage(topLevelQueryLanguage, this.props.queryLanguage);
	// suffix of ':2' indicates that the output of the nested state machine should be JSON
	// suffix is only applicable when waiting for a nested state machine to complete (RUN_JOB)
	// https://docs.aws.amazon.com/step-functions/latest/dg/connect-stepfunctions.html
	const suffix = this.integrationPattern === sfn.IntegrationPattern.RUN_JOB ? ':2' : '';
	let input: any;
	if (this.props.associateWithParent) {
	const associateWithParentEntry = {
	AWS_STEP_FUNCTIONS_STARTED_BY_EXECUTION_ID: queryLanguage === sfn.QueryLanguage.JSONATA
	? '{% $states.context.Execution.Id %}'
	: sfn.JsonPath.stringAt('$$.Execution.Id'),
	};
	input = this.props.input ? { ...this.props.input.value, ...associateWithParentEntry } : associateWithParentEntry;
	} else {
	input = this.props.input ? this.props.input.value: sfn.TaskInput.fromJsonPathAt('$').value;
	}
	return {
	Resource: `${integrationResourceArn('states', 'startExecution', this.integrationPattern)}${suffix}`,
	...this._renderParametersOrArguments({
	Input: input,
	StateMachineArn: this.props.stateMachine.stateMachineArn,
	Name: this.props.name,
	}, queryLanguage),
	};
	}

Agree that null values should be accepted as valid input. The fix likely involves ensuring the internal parameter rendering logic correctly handles null values, similar to the previous implementation.

Just checked PR #34295 while it fixes a related bug concerning null handling within the containsTaskToken check (which could affect StepFunctionsStartExecution in some scenarios), it doesn't seem to address the specific TypeError occurring during parameter rendering that was reported in this issue. The underlying problem in _renderParametersOrArguments likely still exists. We'll immediately bring this up to the team for review.

[pahud]

Reproduction

import * as cdk from 'aws-cdk-lib';
import { Construct } from 'constructs';
import * as sfn from 'aws-cdk-lib/aws-stepfunctions';
import * as tasks from 'aws-cdk-lib/aws-stepfunctions-tasks';

// Renamed class to match the filename expected by cdk init
export class Issue34293ReproStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    // Target state machine (remains the same)
    const definition = new sfn.Pass(this, "Test step");
    const stateMachine = new sfn.StateMachine(this, 'Steps', {
      definitionBody: sfn.DefinitionBody.fromChainable(definition),
    });

    // The problematic task (remains the same)
    const task = new tasks.StepFunctionsStartExecution(this, 'Start migration process', {
      stateMachine: stateMachine,
      integrationPattern: sfn.IntegrationPattern.WAIT_FOR_TASK_TOKEN,
      input: sfn.TaskInput.fromObject({
        token: sfn.JsonPath.taskToken,
        nullProperty: null, // The problematic null value
      }),
    });

    // *** Add this: Define a state machine that USES the task ***
    new sfn.StateMachine(this, 'MainStateMachineThatUsesTask', {
      definitionBody: sfn.DefinitionBody.fromChainable(task), // Use 'task' here
    });
  }
}

On cdk synth

TypeError: Cannot convert undefined or null to object

This exists in 2.186.0.

While in 2.177.0 cdk synth with no error.

Confirmed a regression.