message: make the error layers optional
diff: @@ -258,7 +258,7 @@ void evaluateLayerRmseAtPoses(
  std::vector<utils::VoxelEvaluationDetails>* voxel_evaluation_details_vector,
  std::vector<std::pair<typename voxblox::Layer<VoxelType>::Ptr,
  typename voxblox::Layer<VoxelType>::Ptr>>*
  - aligned_objects_and_error_layers) {
  + aligned_objects_and_error_layers = nullptr) {
  CHECK_NOTNULL(voxel_evaluation_details_vector);
  // Check if world TSDF layer agrees with merged object at all object poses.
  @@ -306,7 +306,7 @@ void evaluateLayerRmseAtPoses(
  std::vector<utils::VoxelEvaluationDetails>* voxel_evaluation_details_vector,
  std::vector<std::pair<typename voxblox::Layer<VoxelType>::Ptr,
  typename voxblox::Layer<VoxelType>::Ptr>>*
  - aligned_objects_and_error_layers) {
  + aligned_objects_and_error_layers = nullptr) {
  CHECK_NOTNULL(voxel_evaluation_details_vector);
  std::vector<Transformation> kindr_transforms_W_O;
  for (const Eigen::Matrix<float, 4, 4>& transform_W_O : transforms_W_O) {
  