Fix empty sequence in moveit_setup_assistant

[DLu]

Description

There's a bug right now in the generation of fake_controllers.yaml such that if no poses are found, it will output invalid yaml.

initial:  # Define initial robot poses.
#  - group: right_arm
#    pose: home

(and then the end of the file)

This results in a cryptic error like

load_parameters: unable to set parameters (last param was [/controller_list=[SNIP]]): cannot marshal None unless allow_none is enabled

With this PR, it now generates

initial:  # Define initial robot poses.
  []
#  - group: group
#    pose: home

Checklist

• Required by CI: Code is auto formatted using clang-format
• Extend the tutorials / documentation reference
• Document API changes relevant to the user in the MIGRATION.md notes
• Create tests, which fail without this PR reference
• Include a screenshot if changing a GUI
• While waiting for someone to review your request, please help review another open pull request to support the maintainers

[davetcoleman]

Not required for approval but @mohmadAyman adding this feature during his GSoC program 7097464

[gavanderhoorn]

This is similar to #1680.

[codecov]

Codecov Report

Merging #2406 (e22daa8) into master (382aa5a) will decrease coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2406      +/-   ##
==========================================
- Coverage   60.22%   60.20%   -0.01%     
==========================================
  Files         352      352              
  Lines       26402    26402              
==========================================
- Hits        15898    15893       -5     
- Misses      10504    10509       +5     

Impacted Files	Coverage Δ
...t_setup_assistant/src/tools/moveit_config_data.cpp	19.21% <ø> (ø)
moveit_core/robot_model/src/joint_model_group.cpp	62.97% <0.00%> (-2.46%)	⬇️
...e/src/parameterization/model_based_state_space.cpp	70.40% <0.00%> (-2.39%)	⬇️
...nning_scene_monitor/src/planning_scene_monitor.cpp	68.16% <0.00%> (-0.15%)	⬇️
...meterization/work_space/pose_model_state_space.cpp	85.30% <0.00%> (+0.74%)	⬆️
.../ompl_interface/src/detail/constrained_sampler.cpp	60.00% <0.00%> (+17.15%)	⬆️

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[rhaschke]

Would be nice, if the empty list would follow the commented example, like this:

initial:  # Define initial robot poses.
#  - group: group
#    pose: home
  []

[tylerjw]

I tested this and it works as described.

[mayman99]

Thanks for fixing it!