Empty Default Value ROS2 Launch Failure

[nfs-chris]

When running ros2 launch azure_kinect_ros_driver driver.launch.py a TypeError gets thrown due to empty default values in DeclareLaunchArgument (sensor_sn and recording_file):

Task exception was never retrieved
future: <Task finished name='Task-2' coro=<LaunchService._process_one_event() done, defined at /opt/ros/foxy/lib/python3.8/site-packages/launch/launch_service.py:226> exception=TypeError("Allowed value types are bytes, bool, int, float, str, Sequence[bool], Sequence[int], Sequence[float], Sequence[str]. Got <class 'NoneType'>.If the parameter is meant to be a string, try wrapping it in launch_ros.parameter_descriptions.ParameterValue(value, value_type=str)")>
Traceback (most recent call last):
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_service.py", line 228, in _process_one_event
    await self.__process_event(next_event)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/launch_service.py", line 248, in __process_event
    visit_all_entities_and_collect_futures(entity, self.__context))
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/utilities/visit_all_entities_and_collect_futures_impl.py", line 45, in visit_all_entities_and_collect_futures
    futures_to_return += visit_all_entities_and_collect_futures(sub_entity, context)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/utilities/visit_all_entities_and_collect_futures_impl.py", line 45, in visit_all_entities_and_collect_futures
    futures_to_return += visit_all_entities_and_collect_futures(sub_entity, context)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/utilities/visit_all_entities_and_collect_futures_impl.py", line 45, in visit_all_entities_and_collect_futures
    futures_to_return += visit_all_entities_and_collect_futures(sub_entity, context)
  [Previous line repeated 1 more time]
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/utilities/visit_all_entities_and_collect_futures_impl.py", line 38, in visit_all_entities_and_collect_futures
    sub_entities = entity.visit(context)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch/action.py", line 108, in visit
    return self.execute(context)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch_ros/actions/node.py", line 444, in execute
    self._perform_substitutions(context)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch_ros/actions/node.py", line 399, in _perform_substitutions
    evaluated_parameters = evaluate_parameters(context, self.__parameters)
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch_ros/utilities/evaluate_parameters.py", line 160, in evaluate_parameters
    output_params.append(evaluate_parameter_dict(context, param))
  File "/opt/ros/foxy/lib/python3.8/site-packages/launch_ros/utilities/evaluate_parameters.py", line 95, in evaluate_parameter_dict
    raise TypeError(
TypeError: Allowed value types are bytes, bool, int, float, str, Sequence[bool], Sequence[int], Sequence[float], Sequence[str]. Got <class 'NoneType'>.If the parameter is meant to be a string, try wrapping it in launch_ros.parameter_descriptions.ParameterValue(value, value_type=str)

Adding .perform(context) to the LaunchConfigurations in driver.launch.py, similar to this fix might fix this.

[ghanim-mukhtar]

I confirm the same issue here with Ubuntu 20.04 focal and foxy, love to have a fix for this.

[ghanim-mukhtar]

I was able to overcome this error by modifying the syntax of the launch file as follows (for both parameters sensor_sn and recording_file:

default_value="''",