Fallback to merge-base if commit hash is invalid

Jenkinsfile

@@ -307,8 +307,14 @@ void checkE2EIgnoreFiles() {
         echo "This is the first run. Using merge base as the starting point for the diff."
         changedFiles = sh(script: "git diff --name-only \$(git merge-base HEAD origin/$CHANGE_TARGET)", returnStdout: true).trim().split('\n').findAll{it}
     } else {
-        echo "Processing changes since last processed commit: $lastProcessedCommitHash"
-        changedFiles = sh(script: "git diff --name-only $lastProcessedCommitHash HEAD", returnStdout: true).trim().split('\n').findAll{it}
+        def commitExists = sh(script: "git cat-file -e $lastProcessedCommitHash 2>/dev/null", returnStatus: true) == 0
+        if (commitExists) {
+            echo "Processing changes since last processed commit: $lastProcessedCommitHash"
+            changedFiles = sh(script: "git diff --name-only $lastProcessedCommitHash HEAD", returnStdout: true).trim().split('\n').findAll{it}
+        } else {
+            echo "Commit hash $lastProcessedCommitHash does not exist in the current repository. Using merge base as the starting point for the diff."
+            changedFiles = sh(script: "git diff --name-only \$(git merge-base HEAD origin/$CHANGE_TARGET)", returnStdout: true).trim().split('\n').findAll{it}
+        }
     }
 
     echo "Excluded files: $excludedFiles"