Safely destructure custom agents response to handle null/undefined. Fix https://github.com/microsoft/vscode/issues/274437

src/platform/github/common/githubService.ts

@@ -341,7 +341,7 @@ export class BaseOctoKitService {
 		return getPullRequestFromGlobalId(this._fetcherService, this._logService, this._telemetryService, this._capiClientService.dotcomAPIURL, token, globalId);
 	}
 
-	protected async getCustomAgentsWithToken(owner: string, repo: string, token: string): Promise<GetCustomAgentsResponse> {
+	protected async getCustomAgentsWithToken(owner: string, repo: string, token: string): Promise<GetCustomAgentsResponse | undefined> {
 		const queryParams = '?exclude_invalid_config=true';
 		return makeGitHubAPIRequest(this._fetcherService, this._logService, this._telemetryService, 'https://api.githubcopilot.com', `agents/swe/custom-agents/${owner}/${repo}${queryParams}`, 'GET', token, undefined, undefined, 'json', 'vscode-copilot-chat');
 	}

src/platform/github/common/octoKitServiceImpl.ts

@@ -148,7 +148,7 @@ export class OctoKitService extends BaseOctoKitService implements IOctoKitServic
 		if (!authToken) {
 			return [];
 		}
-		const { agents } = await this.getCustomAgentsWithToken(owner, repo, authToken);
+		const { agents } = (await this.getCustomAgentsWithToken(owner, repo, authToken)) ?? {};
 		if (!Array.isArray(agents)) {
 			return [];
 		}