troubleshooting.md

@@ -19,4 +19,9 @@ Topic, Service, Action not working
 * Check the types and names are correct (they should match what you get from `ros2 topic`, `ros2 service` and `ros2 action` commands).
 * Check the node is spinning, i.e., that it was added to an executor, that the executor is spinning.
 * If making a service/action call from a callback, make sure you are using a `MultiThreadedExecutor` and that `ReentrantGroup` are set correctly.
-* Make sure that you are not that not using `rclpy.spin*` functions with a custom created executor.
+* Make sure that you are not that not using `rclpy.spin*` functions with a custom created executor.
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+
+Strange errors
+--------------
+
+* When calling `self.executor.add_node` you get the error `Cannot call 'add_node' on object of type NoneType`. Try renaming `self.executor` to `self.executor_`. This might be caused by some conflicts with a base class.
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