fix(rebaser): handle 'Reference does not exist' error

 Specific error handling for the "Reference does not exist" error was added in the `rebaser.ts` file to prevent the GitHub Action from failing when a referenced branch or commit does not exist. A corresponding test was implemented in `rebaser.test.ts` to ensure this error is handled gracefully. Additionally, the CHANGELOG.md was updated to document the fix.

Author: jetbrains-junie[bot]

CHANGELOG.md

@@ -1,5 +1,11 @@
 # Changelog
 
+## Unreleased
+
+### Bug Fixes
+
+- Added handling for "Reference does not exist" error during rebasing to prevent action failures when a reference (branch or commit) no longer exists
+
 ## v0.2.0 (2025-08-05)
 
 ### Dependencies Updated

src/Rebaser/__tests__/rebaser.test.ts

@@ -81,6 +81,33 @@ test('Failing rebase due to head base change completes successfully', async () =
     expect(error).toBeNull();
 });
 
+test('Failing rebase due to reference not existing completes successfully', async () => {
+    /* Given */
+    testGithubRebase.result = Promise.reject('HttpError: Reference does not exist');
+
+    let error = null;
+
+    /* When */
+    try {
+        await rebaser.rebasePullRequests([
+            {
+                ownerName: 'owner',
+                repoName: 'repo',
+                number: 3,
+                draft: false,
+                rebaseable: true,
+                mergeableState: 'behind',
+                labels: [],
+            },
+        ]);
+    } catch (e) {
+        error = e;
+    }
+
+    /* Then */
+    expect(error).toBeNull();
+});
+
 test('Failing rebase due unknown failure errors', async () => {
     /* Given */
     testGithubRebase.result = Promise.reject('Some unknown error');

src/Rebaser/rebaser.ts

@@ -30,6 +30,10 @@ export class Rebaser {
                 warning(`Rebase aborted because the head branch changed for ${JSON.stringify(pullRequest)}`);
                 return;
             }
+            if (String(e).includes('Reference does not exist')) {
+                warning(`Reference does not exist for ${JSON.stringify(pullRequest)}. The branch may have been deleted or modified.`);
+                return;
+            }
             throw new Error(`Error while rebasing for ${JSON.stringify(pullRequest)}: ${String(e)}`);
         }
     }