Abort when there are no op registered.

mace/core/net.cc

@@ -23,7 +23,9 @@ SimpleNet::SimpleNet(const std::shared_ptr<const NetDef>& net_def,
     std::unique_ptr<OperatorBase> op{nullptr};
     OperatorDef temp_def(operator_def);
     op = CreateOperator(temp_def, ws, type);
-    operators_.emplace_back(std::move(op));
+    if (!op) {
+      operators_.emplace_back(std::move(op));
+    }
   }
 }
 bool SimpleNet::Run() {

mace/core/registry.h

@@ -26,8 +26,7 @@ class Registry {
 
   unique_ptr<ObjectType> Create(const SrcType& key, Args... args) {
     if (registry_.count(key) == 0) {
-      VLOG(2) << "Key not registered: " << key;
-      return nullptr;
+      LOG(FATAL) << "Key not registered: " << key;
     }
     return registry_[key](args...);
   }