Sync backport changelog action: Use outputs instead of env (#63792)

* Sync backport changelog action: Use outputs instead of env

* Default empty issue body to ''

Co-authored-by: noisysocks <[email protected]>
Co-authored-by: talldan <[email protected]>

.github/workflows/sync-backport-changelog.yml

@@ -14,10 +14,11 @@ jobs:
               with:
                   fetch-depth: 2 # Fetch the last two commits to compare changes
             - name: Check for changes in backport-changelog
+              id: check-for-changes
               run: |
-                  git diff --quiet HEAD^ HEAD -- backport-changelog || echo "changes=true" >> $GITHUB_OUTPUT
+                  git diff --quiet HEAD^ HEAD -- backport-changelog || echo "HAS_CHANGES=1" >> "$GITHUB_OUTPUT"
             - name: Sync Issue
-              if: env.changes == 'true'
+              if: steps.check-for-changes.outputs.HAS_CHANGES
               uses: actions/github-script@60a0d83039c74a4aee543508d2ffcb1c3799cdea # v7.0.1
               with:
                   script: |
@@ -52,18 +53,20 @@ jobs:
                       const endDelimiter = '<!-- END TRUNK BACKPORT CHANGELOG -->';
                       const autoGeneratedContent = `${startDelimiter}\n${processedChangelog}\n${endDelimiter}`;
 
-                      const regex = new RegExp(`${startDelimiter}[\\s\\S]*${endDelimiter}`);
+                      const existingBody = latestIssue.body ?? '';
+
                       let newBody;
 
-                      if (regex.test(latestIssue.body)) {
+                      const regex = new RegExp(`${startDelimiter}[\\s\\S]*${endDelimiter}`);
+                      if (regex.test(existingBody)) {
                         // If delimiters exist, replace the content between them
-                        newBody = latestIssue.body.replace(regex, autoGeneratedContent);
+                        newBody = existingBody.replace(regex, autoGeneratedContent);
                       } else {
                         // If delimiters don't exist, append the new content at the end
-                        newBody = `${latestIssue.body}\n\n${autoGeneratedContent}`;
+                        newBody = `${existingBody}\n\n${autoGeneratedContent}`;
                       }
 
-                      if (newBody.trim() !== latestIssue.body.trim()) {
+                      if (newBody.trim() !== existingBody.trim()) {
                         await github.rest.issues.update({
                           owner: context.repo.owner,
                           repo: context.repo.repo,