fix: fix param base name which starts with '.'

[wep21]

param base name which starts with '.' causes the problem for parameter as below.

❯ ros2 param dump /sensing/camera/camera1/rectify_node
/sensing/camera/camera1/rectify_node:
  ros__parameters:
    ? ''
    : image_rect:
        format: jpeg
        jpeg_quality: 95
        png_level: 3
    interpolation: 1
    qos_overrides:
      /parameter_events:
        publisher:
          depth: 1000
          durability: volatile
          history: keep_last
          reliability: reliable
    queue_size: 5
    use_sim_time: false
    use_system_default_qos: false

[wep21]

FYI @mjcarroll @gbiggs

[gbiggs]

Please post a clearer example and explanation of what the error is?

[wep21]

@gbiggs I found out the output of ros2 param dump seems wrong, but I cannot reproduce it again, so I close this PR once.

• wrong

  ros__parameters:
    ? ''
    : image_rect:
        format: jpeg
        jpeg_quality: 95
        png_level: 3

• correct

/sensing/camera/camera0/rectify_node:
  ros__parameters:
    image_rect:
      format: jpeg
      jpeg_quality: 80
      png_level: 3

If I come across this problem again, I will reopen this PR.

[wep21]

@gbiggs I confirmed that a parameter starts with '.' causes the problem. I have tested with parameter blackboard.

• set .aaa parameter
  ros2 param set /parameter_blackboard .aaa 200
• .aaa parameter dumped on the screen seems wrong. Also I can't get parameter from .aaa.

❯ ros2 param dump --print /parameter_blackboard
/parameter_blackboard:
  ros__parameters:
    ? ''
    : aaa: 200
    qos_overrides:
      /parameter_events:
        publisher:
          depth: 1000
          durability: volatile
          history: keep_last
          reliability: reliable
    use_sim_time: false

Do you think this PR should be reopened?

[gbiggs]

So it turns out that dots in parameter names are used for namespace separation in a number of places. This means that we can't consider a dot to be a valid character in a parameter name.

There is an old proposal to change this, but it didn't get implemented. I suggest you resurrect that if you want move forward with this idea.
ros2/design#241