Bug report

Required Info:

• Operating System:
  • Ubuntu 22.04/Ubuntu 20.04
• ROS2 Version:
  • Humble/Rolling/Galactic/
• Version or commit hash:
  • 10cd1a1
• DDS implementation:
  • Default of ROS2

Steps to reproduce issue

ros2 launch nav2_bringup multi_tb3_simulation_launch.py

Expected behavior

Multi robot simulation launches properly without errors

Actual behavior

Everything else starts up, but the controllers crash and navigation does not work. The exact failure messages are:

[controller_server-8]   what():  parameter 'goal_checker_plugins' has invalid type: Wrong parameter type, parameter {goal_checker_plugins} is of type {string_array}, setting it to {string} is not allowed.
...
[ERROR] [controller_server-8]: process has died [pid 132737, exit code -6,

This is repeated for every robot launched.

Additional information

As the message reports, the goal_checker_plugins should be declared as a list of strings in the param files here and here, but are declared as single strings only.

The fix is to enclose the string values in square brackets. If this solution is acceptable, I can make PRs.