Use optional of reference wrapper

rmf_fleet_adapter/include/rmf_fleet_adapter/agv/RobotUpdateHandle.hpp

@@ -28,6 +28,7 @@
 
 #include <vector>
 #include <memory>
+#include <functional>
 
 namespace rmf_fleet_adapter {
 namespace agv {
@@ -101,7 +102,8 @@ class RobotUpdateHandle
   rmf_utils::optional<rmf_traffic::Duration> maximum_delay() const;
 
   /// Get the schedule participant of this robot
-  rmf_traffic::schedule::Participant& get_participant();
+  rmf_utils::optional<std::reference_wrapper<rmf_traffic::schedule::Participant>>
+    get_participant();
 
   class Implementation;
 private:

rmf_fleet_adapter/src/full_control/main.cpp

@@ -302,9 +302,10 @@ class FleetDriverRobotCommandHandle
           rmf_traffic_ros2::convert(state.location.t),
           positions);
 
-      auto& participant = _travel_info.updater->get_participant();
-      participant.set(
-          {rmf_traffic::Route{state.location.level_name, trajectory}});
+      auto participant = _travel_info.updater->get_participant();
+      if (participant)
+        participant.value().get().set(
+            {rmf_traffic::Route{state.location.level_name, trajectory}});
     }
     else
     {

rmf_fleet_adapter/src/rmf_fleet_adapter/agv/RobotUpdateHandle.cpp

@@ -189,14 +189,15 @@ RobotUpdateHandle::maximum_delay() const
 }
 
 //==============================================================================
-rmf_traffic::schedule::Participant&
-RobotUpdateHandle::get_participant()
+rmf_utils::optional<std::reference_wrapper<rmf_traffic::schedule::Participant>>
+  RobotUpdateHandle::get_participant()
 {
   if (const auto context = _pimpl->get_context())
   {
     auto& itinerary = context->itinerary();
     return itinerary;
   }
+  return rmf_utils::nullopt;
 }
 
 //==============================================================================