Fix nil pointer exception in handleIssueCommentEvent when GitHub App installation is missing.

Signed-off-by: Lorenzo Buitizon <[email protected]>

Author: MrKeiKun

backend/controllers/github_comment.go

@@ -78,6 +78,45 @@ func handleIssueCommentEvent(gh utils.GithubClientProvider, payload *github.Issu
 		)
 		return fmt.Errorf("error getting github app link")
 	}
+	if link == nil {
+		slog.Error("GitHub app installation link not found",
+			"installationId", installationId,
+		)
+
+		// Try to get GitHub service to post error comment
+		ghService, _, ghServiceErr := utils.GetGithubService(gh, installationId, repoFullName, repoOwner, repoName)
+		if ghServiceErr != nil {
+			slog.Error("Error getting GitHub service to post error comment",
+				"installationId", installationId,
+				"repoFullName", repoFullName,
+				"error", ghServiceErr,
+			)
+			return fmt.Errorf("github app installation link not found and could not post error comment")
+		}
+
+		// Post helpful error message to the user
+		errorMsg := ":x: **Digger could not find the GitHub App installation record.**\n\n" +
+			"This usually happens when:\n" +
+			"• The GitHub App was not installed successfully\n" +
+			"• The installation process did not complete the callback to Digger\n" +
+			"• There was an issue with the GitHub App installation flow\n\n" +
+			"Please ensure that:\n" +
+			"1. The GitHub App is properly installed on your repository\n" +
+			"2. The installation completed successfully and redirected to the callback URL\n" +
+			"3. The repository is accessible to the GitHub App\n\n" +
+			"If the issue persists, please contact support with this installation ID: " + fmt.Sprintf("%d", installationId)
+
+		_, commentErr := ghService.PublishComment(issueNumber, errorMsg)
+		if commentErr != nil {
+			slog.Error("Error posting installation not found comment",
+				"issueNumber", issueNumber,
+				"error", commentErr,
+			)
+			return fmt.Errorf("github app installation link not found and could not post error comment")
+		}
+
+		return fmt.Errorf("github app installation link not found")
+	}
 	orgId := link.OrganisationId
 
 	if *payload.Action != "created" {