diff --git a/app/Services/InquiryService.php b/app/Services/InquiryService.php
index bed9b88..4f56716 100644
--- a/app/Services/InquiryService.php
+++ b/app/Services/InquiryService.php
@@ -182,7 +182,7 @@ class InquiryService extends BaseService
             $data = array();
             $data['user_id'] = $user_info['user_id'];
             $data['patient_id'] = $user_info['client_user_id'];
-            $data['doctor_id'] = $request_params['doctor_id'] ?? "";
+            $data['doctor_id'] = $request_params['doctor_id'] ?? null;
             $data['family_id'] = $request_params['family_id'];
             $data['inquiry_type'] = $request_params['inquiry_type'];
             $data['inquiry_mode'] = $request_params['inquiry_mode'];