Effect of "defaultvalue" in config.json?

[Jens Nestel]

Is there a definition when the "defaultvalue" in config.json is applied?

I have tried explicitly handing over input_str=None, as well as omitting input_str when calling writer_plugin.
In both cases the writer_plugin did not seem to fall back to the "defaultvalue" I had inserted in config.json for this test.

At least gpt-3.5-turbo takes the prompt for a poem about an undefined variable with humor : "A cat chasing its own tail"