[*] cascade errors here plox

Source/Async/WorkItem.cpp

@@ -68,6 +68,12 @@ namespace Aurora::Async
     {
         for (auto &workItem : workItems)
         {
+            if (!workItem)
+            {
+                SysPushErrorArg();
+                return false;
+            }
+
             auto dependency = AuReinterpretCast<WorkItem>(workItem);
             AU_LOCK_GUARD(dependency->lock);
 
@@ -111,6 +117,11 @@ namespace Aurora::Async
     AuSPtr<IWorkItem> WorkItem::Then(const AuSPtr<IWorkItem> &next)
     {
         auto that = AU_SHARED_FROM_THIS;
+        if (!next)
+        {
+            SysPushErrorArg();
+            return {};
+        }
         next->WaitFor(that);
         next->Dispatch();
         return that;