fix(autoware_crosswalk_traffic_light_estimator) : add process that guard access to empty elements.

Signed-off-by: k-hazama-esol <k-hazama@esol.co.jp>

Author: k-hazama-esol

perception/autoware_crosswalk_traffic_light_estimator/src/node.cpp

@@ -303,7 +303,11 @@ void CrosswalkTrafficLightEstimatorNode::setCrosswalkTrafficSignal(
         output_traffic_signal_element.color = color;
         output_traffic_signal_element.shape = TrafficSignalElement::CIRCLE;
         output_traffic_signal_element.confidence = 1.0;
-        output.traffic_light_groups[idx].elements[0] = output_traffic_signal_element;
+        if (output.traffic_light_groups[idx].elements.empty()) {
+          output.traffic_light_groups[idx].elements.push_back(output_traffic_signal_element);
+        } else {
+          output.traffic_light_groups[idx].elements[0] = output_traffic_signal_element;
+        }
         continue;
       }
       updateFlashingState(signal);  // check if it is flashing
@@ -325,6 +329,10 @@ void CrosswalkTrafficLightEstimatorNode::setCrosswalkTrafficSignal(
 bool CrosswalkTrafficLightEstimatorNode::isInvalidDetectionStatus(
   const TrafficSignal & signal) const
 {
+   // invalid if elements is empty
+  if (signal.elements.empty()) {
+    return true;
+  }
   // check occlusion, backlight(shape is unknown) and no detection(shape is circle)
   if (
     signal.elements.front().color == TrafficSignalElement::UNKNOWN &&
@@ -347,6 +355,7 @@ void CrosswalkTrafficLightEstimatorNode::updateFlashingState(const TrafficSignal
 
   // flashing green
   if (
+    !signal.elements.empty() &&
     signal.elements.front().color == TrafficSignalElement::UNKNOWN &&
     signal.elements.front().confidence != 0 &&  // not due to occlusion
     current_color_state_.at(id) != TrafficSignalElement::UNKNOWN) {