fix(CLI): change-set diff not required for new stack diffs

packages/@aws-cdk/cloudformation-diff/lib/diff-template.ts

@@ -51,9 +51,12 @@ export function fullDiff(
   normalize(currentTemplate);
   normalize(newTemplate);
   const theDiff = diffTemplate(currentTemplate, newTemplate);
+  // If the currentTemplate is empty, we skip these changeset functions.
   if (changeSet) {
-    filterFalsePositivies(theDiff, changeSet);
     addImportInformation(theDiff, changeSet);
+    if (Object.keys(currentTemplate).length > 0) {
+      filterFalsePositivies(theDiff, changeSet);
+    }
   }
 
   return theDiff;

packages/@aws-cdk/cloudformation-diff/test/diff-template.test.ts

@@ -1231,4 +1231,22 @@ describe('changeset', () => {
     expect(differences.resources.differenceCount).toBe(1);
     expect(differences.resources.get('BucketResource').changeImpact === ResourceImpact.WILL_IMPORT);
   });
+
+  test('does not do changeset checks for new stack', async () => {
+    // GIVEN
+    const currentTemplate = {};
+
+    // WHEN
+    const newTemplate = {
+      Resources: {
+        NewResource: {
+          Type: 'AWS::Something::Resource',
+        },
+      },
+    };
+
+    let differences = fullDiff(currentTemplate, newTemplate);
+    expect(differences.resources.differenceCount).toBe(1);
+    expect(differences.resources.get('NewResource').changeImpact).toBe(ResourceImpact.WILL_CREATE);
+  });
 });