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

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

@@ -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-lib/aws-s3-deployment/lib/render-data.ts

@@ -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.

packages/aws-cdk-lib/aws-s3-deployment/test/content.test.ts

@@ -111,3 +111,30 @@ test('lazy within a string is not resolved', () => {
     },
   });
 });
+
+test('renderData can render empty string data', () => {
+  const stack = new Stack();
+  expect(renderData('')).toStrictEqual({
+    markers: {},
+    text: '',
+  });
+});
+
+test('Source.data with empty string does not throw error', () => {
+  const stack = new Stack();
+  const handler = new lambda.Function(stack, 'Handler', {
+    runtime: lambda.Runtime.NODEJS_LATEST,
+    code: lambda.Code.fromInline('foo'),
+    handler: 'index.handler',
+  });
+
+  // This is the exact reproduction case from issue #35809
+  // Before the fix, this would throw: "The "data" argument must be of type string... Received undefined"
+  expect(() => {
+    const source = Source.data('path/to/empty', '');
+    const actual = source.bind(stack, { handlerRole: handler.role! });
+    expect(actual.markers).toStrictEqual({});
+    expect(actual.bucket).toBeDefined();
+    expect(actual.zipObjectKey).toBeDefined();
+  }).not.toThrow();
+});