fix(s3-deployment): Source.jsonData() fails with null JSON values (#36054)

In cdk-lib aws-s3-deployment, creating a Source.jsonData() will fail if the JSON has any null fields in it due to `escapeTokens` trying to build an object from it, resulting in `TypeError: Cannot convert undefined or null to object`

### Issue # (if applicable)

Closes #36052.

### Reason for this change

Can't create a Source.jsonData() when `null` values are present in the JSON data itself

### Description of changes

Added a null check around `escapeTokens()` to prevent it from trying to process `null` values

### Describe any new or updated permissions being added

N/A


### Description of how you validated changes

Tested by hand via modifying the compiled JS in my project to add the check, and was able to successfully upload a JSON file to S3 with a null value contained inside. Also added coverage via unit tests/integration tests for the PR build to chew through.

### Checklist
- [X] My code adheres to the [CONTRIBUTING GUIDE](https://github.com/aws/aws-cdk/blob/main/CONTRIBUTING.md) and [DESIGN GUIDELINES](https://github.com/aws/aws-cdk/blob/main/docs/DESIGN_GUIDELINES.md)

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: Lukanite

packages/@aws-cdk-testing/framework-integ/test/aws-s3-deployment/test/integ.bucket-deployment-data.js.snapshot/asset.8de7dc173740857dd772ca214c7ac8381483f7ee406d94fb9ff9e95ad407d876/my-json/config-with-null.json

@@ -218,6 +218,9 @@
      {
       "Fn::Sub": "cdk-hnb659fds-assets-${AWS::AccountId}-${AWS::Region}"
      },
+     {
+      "Fn::Sub": "cdk-hnb659fds-assets-${AWS::AccountId}-${AWS::Region}"
+     },
      {
       "Fn::Sub": "cdk-hnb659fds-assets-${AWS::AccountId}-${AWS::Region}"
      }
@@ -230,7 +233,8 @@
      "4ba8cfb53da242e91a423f3333c95db70ac0b5c2481a2d7e5c51142e5738403f.zip",
      "4458891c23c9754723db261b607985ee4fce5a087343fca93e9608fb49e083ba.zip",
      "c3f91ed893cc759513d80ebd56bcaae5061b08bff3dd8ad10daeb62558bac52e.zip",
-     "10cb9bf43614add407e699e4af8e1ba4a9789363f48fa816662b15885c354e1a.zip"
+     "10cb9bf43614add407e699e4af8e1ba4a9789363f48fa816662b15885c354e1a.zip",
+     "8de7dc173740857dd772ca214c7ac8381483f7ee406d94fb9ff9e95ad407d876.zip"
     ],
     "SourceMarkers": [
      {},
@@ -334,6 +338,7 @@
        ]
       }
      },
+     {},
      {}
     ],
     "SourceMarkersConfig": [
@@ -346,6 +351,7 @@
       "jsonEscape": true
      },
      {},
+     {},
      {}
     ],
     "DestinationBucketName": {

packages/@aws-cdk-testing/framework-integ/test/aws-s3-deployment/test/integ.bucket-deployment-data.js.snapshot/asset.c11608a15785084ea1afe65826e575ee316add10c8b1bb373e93297e26aec564.bundle/index.js renamed to packages/@aws-cdk-testing/framework-integ/test/aws-s3-deployment/test/integ.bucket-deployment-data.js.snapshot/asset.ca235e6258b11c240506ff06f79037eca461b8d0d9464a947a386d38d8163515.bundle/index.js

@@ -64,6 +64,9 @@ class TestBucketDeploymentData extends Stack {
     // Test empty string handling
     const file8 = Source.data('file8.txt', '');
 
+    // Test null JSON data value
+    const file9 = Source.jsonData('my-json/config-with-null.json', { hello: 'there', goodbye: null });
+
     const deployment = new BucketDeployment(this, 'DeployWithDataSources', {
       destinationBucket: this.bucket,
       sources: [file1, file2],
@@ -77,6 +80,7 @@ class TestBucketDeploymentData extends Stack {
     deployment.addSource(file6);
     deployment.addSource(file7);
     deployment.addSource(file8);
+    deployment.addSource(file9);
 
     new CfnOutput(this, 'BucketName', { value: this.bucket.bucketName });
   }
@@ -105,6 +109,17 @@ assertionProvider.expect(ExpectedResult.objectLike({
   Body: '{"secret_value":"test\\"with\\"quotes"}',
 }));
 
+// Assert that JSON data with a null value is represented properly
+const jsonNullAssertionProvider = integTest.assertions.awsApiCall('S3', 'getObject', {
+  Bucket: testCase.bucket.bucketName,
+  Key: path.join('deploy/here', 'my-json/config-with-null.json'),
+});
+
+// Verify the content is valid JSON and both null and non-null fields are present
+jsonNullAssertionProvider.expect(ExpectedResult.objectLike({
+  Body: '{"hello":"there","goodbye":null}',
+}));
+
 // Add assertions to verify the YAML file
 const yamlAssertionProvider = integTest.assertions.awsApiCall('S3', 'getObject', {
   Bucket: testCase.bucket.bucketName,

packages/@aws-cdk-testing/framework-integ/test/aws-s3-deployment/test/integ.bucket-deployment-data.js.snapshot/integtestbucketdeploymentdataDefaultTestDeployAssert6FF3075D.assets.json

@@ -280,7 +280,7 @@ export class Source {
       return obj.map(v => Source.escapeTokens(scope, v));
     }
 
-    if (typeof obj === 'object') {
+    if (obj !== null && typeof obj === 'object') {
       return Object.fromEntries(
         Object.entries(obj).map(([key, value]) => {
           // As JSON keys are always strings, keys are assumed to be either regular strings or string tokens.