Add an error msg if empty message is received (backport #1424) (#1428)

Co-authored-by: Christoph Fröhlich <[email protected]>

joint_trajectory_controller/src/joint_trajectory_controller.cpp

@@ -1531,8 +1531,15 @@ bool JointTrajectoryController::validate_trajectory_msg(
     // This currently supports only position, velocity and acceleration inputs
     if (params_.allow_integration_in_goal_trajectories)
     {
-      const bool all_empty = points[i].positions.empty() && points[i].velocities.empty() &&
-                             points[i].accelerations.empty();
+      if (
+        points[i].positions.empty() && points[i].velocities.empty() &&
+        points[i].accelerations.empty())
+      {
+        RCLCPP_ERROR(
+          get_node()->get_logger(),
+          "The given trajectory has no position, velocity, or acceleration points.");
+        return false;
+      }
       const bool position_error =
         !points[i].positions.empty() &&
         !validate_trajectory_point_field(joint_count, points[i].positions, "positions", i, false);
@@ -1543,7 +1550,7 @@ bool JointTrajectoryController::validate_trajectory_msg(
         !points[i].accelerations.empty() &&
         !validate_trajectory_point_field(
           joint_count, points[i].accelerations, "accelerations", i, false);
-      if (all_empty || position_error || velocity_error || acceleration_error)
+      if (position_error || velocity_error || acceleration_error)
       {
         return false;
       }