Use std::optional for nullable

AIDL now use std::optional to represent nullable types for efficiency
instead of std::unique_ptr which might cause additional heap allocation.

Bug: 1447732670
Test: m
Change-Id: I9045bc6fc2eb06839203af6db94a80de9b83ad1f
diff --git a/services/camera/libcameraservice/hidl/HidlCameraService.cpp b/services/camera/libcameraservice/hidl/HidlCameraService.cpp
index 97ba9c4..b381d6a 100644
--- a/services/camera/libcameraservice/hidl/HidlCameraService.cpp
+++ b/services/camera/libcameraservice/hidl/HidlCameraService.cpp
@@ -103,7 +103,7 @@
     }
     sp<hardware::camera2::ICameraDeviceCallbacks> callbacks = hybridCallbacks;
     binder::Status serviceRet = mAidlICameraService->connectDevice(
-            callbacks, String16(cameraId.c_str()), String16(""), std::unique_ptr<String16>(),
+            callbacks, String16(cameraId.c_str()), String16(""), {},
             hardware::ICameraService::USE_CALLING_UID, /*out*/&deviceRemote);
     HStatus status = HStatus::NO_ERROR;
     if (!serviceRet.isOk()) {