Example launch error with robot arg when using docker composer file

[Joao-G-Martins]

Hello!
I found an error when running the default demo.

When running
docker compose up simple-room-demo
or even when installing all dependencies on my system and running it with
ros2 launch grab2_behavior_tree bt_demo.launch.py robot:=panda world:=table behavior:=collect_cubes
The same that is in the composer file, I get this error:

[ERROR] [launch]: Caught exception in launch (see debug for traceback): local variable 'robot_arg' referenced before assignment

After digging into the launch files, I found out that inside the launch file, there is an if/else with the robot:

 if robot == 'franka':
        robot_arg = 'franka'
        jc_action_arg = '/panda_arm_controller/follow_joint_trajectory'
        gc_action_arg = '/panda_hand_controller/gripper_cmd'

However, in the composer it is like this:

  simple-room-demo:
    extends: grab2
    command: >
      ros2 launch grab2_behavior_tree bt_demo.launch.py
      robot:=panda
      world:=table
      behavior:=collect_cubes

Calling the robot Panda, which is not listed inside the if/else, instead of Franka.

I hope you can fix it so everyone can test it.

Thank you!