fix(s3-deployment): handle empty string in Source.data() (#35824)

### Issue # (if applicable)

Closes #35809.
Original PR: #35818
This PR is been created to fasten release of the fix for the p0

### Reason for this change


`Source.data()` fails with a TypeError when called with an empty string as the data parameter in CDK v2.207.0+. This is a regression from v2.206.0 where empty string deployment worked correctly.

The issue manifests as:
```
TypeError: The "data" argument must be of type string or an instance of Buffer, TypedArray, or DataView. Received undefined
    at Object.writeFileSync (node:fs:2434:5)
```

### Description of changes
This change handles the the case from renderData function.


### Describe any new or updated permissions being added




### Description of how you validated changes
Unit tests have been added to cover this case and integ test has also been updated.



### 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: abidhasan-aws

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

@@ -215,6 +215,9 @@
      {
       "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}"
      }
@@ -226,7 +229,8 @@
      "939a4ab8b51f1a1cccb59d97f04c318ad41c1d404e666c158ca2810894bc5f5f.zip",
      "4ba8cfb53da242e91a423f3333c95db70ac0b5c2481a2d7e5c51142e5738403f.zip",
      "4458891c23c9754723db261b607985ee4fce5a087343fca93e9608fb49e083ba.zip",
-     "c3f91ed893cc759513d80ebd56bcaae5061b08bff3dd8ad10daeb62558bac52e.zip"
+     "c3f91ed893cc759513d80ebd56bcaae5061b08bff3dd8ad10daeb62558bac52e.zip",
+     "10cb9bf43614add407e699e4af8e1ba4a9789363f48fa816662b15885c354e1a.zip"
     ],
     "SourceMarkers": [
      {},
@@ -329,7 +333,8 @@
         ]
        ]
       }
-     }
+     },
+     {}
     ],
     "SourceMarkersConfig": [
      {},
@@ -340,6 +345,7 @@
      {
       "jsonEscape": true
      },
+     {},
      {}
     ],
     "DestinationBucketName": {

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

@@ -50,6 +50,9 @@ const file7 = Source.yamlData('my-yaml/secret-config.yaml', {
   secret_value: tokenizedValue,
 });
 
+// case for empty string
+const file8 = Source.data('file8.txt', '');
+
 const deployment = new BucketDeployment(stack, 'DeployMeHere', {
   destinationBucket: bucket,
   sources: [file1, file2],
@@ -61,6 +64,7 @@ deployment.addSource(file4);
 deployment.addSource(file5);
 deployment.addSource(file6);
 deployment.addSource(file7);
+deployment.addSource(file8);
 
 new CfnOutput(stack, 'BucketName', { value: bucket.bucketName });
 

packages/@aws-cdk-testing/framework-integ/test/aws-s3-deployment/test/integ.bucket-deployment-data.js.snapshot/asset.10cb9bf43614add407e699e4af8e1ba4a9789363f48fa816662b15885c354e1a/file8.txt

@@ -34,6 +34,14 @@ class TokenToMarkerMapper implements ITokenMapper {
 export function renderData(data: string): Content {
   const tokenMapper = new TokenToMarkerMapper();
 
+  // Handle empty string case explicitly to avoid StringConcat.join(undefined, undefined)
+  if (data === '') {
+    return {
+      text: '',
+      markers: {},
+    };
+  }
+
   return {
     // Break down the string into its token fragments and replace each token with a marker.
     // Then rejoin the fragments with basic string concatenation.