Emit warning when fill option is specified but filler plugin is not registered

[kurkle]

Documentation Is:

• Missing or needed?
• Confusing
• Not sure?

Please Explain in Detail...

fill: true silently does nothing when filler is not registered.

Your Proposal for Changes

This would help people understand that the plugin is needed for filling.

Maybe a good place for the warning would be in the initialize function of the controllers (line/radar)?

Example

No response