From 1ace19a48dfe21879aa50f20015e009e0517fef2 Mon Sep 17 00:00:00 2001
From: Paul Gessinger <hello@paulgessinger.com>
Date: Wed, 30 Oct 2024 10:10:32 +0100
Subject: [PATCH] fix: MeasSel error output, config check

---
 Core/include/Acts/TrackFinding/CombinatorialKalmanFilter.hpp | 2 +-
 Core/src/TrackFinding/MeasurementSelector.cpp                | 5 +++++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/Core/include/Acts/TrackFinding/CombinatorialKalmanFilter.hpp b/Core/include/Acts/TrackFinding/CombinatorialKalmanFilter.hpp
index 05e236e1e29..35acbc49feb 100644
--- a/Core/include/Acts/TrackFinding/CombinatorialKalmanFilter.hpp
+++ b/Core/include/Acts/TrackFinding/CombinatorialKalmanFilter.hpp
@@ -399,7 +399,7 @@ class CombinatorialKalmanFilter {
               measurementSelector(trackStateCandidates, isOutlier, logger);
       if (!selectorResult.ok()) {
         ACTS_ERROR("Selection of calibrated measurements failed: "
-                   << selectorResult.error());
+                   << selectorResult.error().message());
         resultTrackStateList =
             ResultTrackStateList::failure(selectorResult.error());
       } else {
diff --git a/Core/src/TrackFinding/MeasurementSelector.cpp b/Core/src/TrackFinding/MeasurementSelector.cpp
index 130c8381536..f3de466f5df 100644
--- a/Core/src/TrackFinding/MeasurementSelector.cpp
+++ b/Core/src/TrackFinding/MeasurementSelector.cpp
@@ -29,6 +29,11 @@ MeasurementSelector::MeasurementSelector(const MeasurementSelectorCuts& cuts)
     : MeasurementSelector({{GeometryIdentifier(), cuts}}) {}
 
 MeasurementSelector::MeasurementSelector(const Config& config) {
+  if (config.empty()) {
+    throw std::invalid_argument(
+        "MeasurementSelector: Configuration must not be empty");
+  }
+
   std::vector<InternalConfig::InputElement> tmp;
   tmp.reserve(config.size());
   for (std::size_t i = 0; i < config.size(); ++i) {