diff --git a/api/dify_graph/nodes/human_input/entities.py b/api/dify_graph/nodes/human_input/entities.py
index 82a8f32053..642c2143e5 100644
--- a/api/dify_graph/nodes/human_input/entities.py
+++ b/api/dify_graph/nodes/human_input/entities.py
@@ -72,8 +72,8 @@ class EmailDeliveryConfig(BaseModel):
     body: str
     debug_mode: bool = False
 
-    def with_debug_recipient(self, user_id: str) -> "EmailDeliveryConfig":
-        if not user_id:
+    def with_debug_recipient(self, user_id: str | None) -> "EmailDeliveryConfig":
+        if user_id is None:
             debug_recipients = EmailRecipients(whole_workspace=False, items=[])
             return self.model_copy(update={"recipients": debug_recipients})
         debug_recipients = EmailRecipients(whole_workspace=False, items=[MemberRecipient(user_id=user_id)])
@@ -141,7 +141,7 @@ def apply_debug_email_recipient(
     method: DeliveryChannelConfig,
     *,
     enabled: bool,
-    user_id: str,
+    user_id: str | None,
 ) -> DeliveryChannelConfig:
     if not enabled:
         return method
@@ -149,7 +149,7 @@ def apply_debug_email_recipient(
         return method
     if not method.config.debug_mode:
         return method
-    debug_config = method.config.with_debug_recipient(user_id or "")
+    debug_config = method.config.with_debug_recipient(user_id)
     return method.model_copy(update={"config": debug_config})
 
 
diff --git a/api/services/workflow_service.py b/api/services/workflow_service.py
index ec37fbeb6b..2549cdf180 100644
--- a/api/services/workflow_service.py
+++ b/api/services/workflow_service.py
@@ -952,7 +952,7 @@ class WorkflowService:
         delivery_method = apply_debug_email_recipient(
             delivery_method,
             enabled=True,
-            user_id=account.id or "",
+            user_id=account.id,
         )
 
         variable_pool = self._build_human_input_variable_pool(