Don't use mutable default argument.

[bpkroth]

If this isn't respected, then additional_configs can be built up overtime when multiple optimizers are created in a single process.

This can occur when the use_default_config option is set True and/or when additional_configs are provided.

When different ConfigSpaces are provided this can result in an error due to mismatched defaults, for instance.

In other cases it can result in non-deterministic behavior due to the random ordering of the configs that get added (e.g., with different parallel pytest runs).

• [x] Cleanup other sources of this error as well elsewhere in the code.
• [x] Add pylint checks for this issue.

[helegraf]

Thanks for spotting and addressing this issue! We will discuss how we want to adapt the pre-commit hooks.

[helegraf]

Could you please add a line to the CHANGELOG.md mentioning the bugfix?

[bpkroth]

Could you please add a line to the CHANGELOG.md mentioning the bugfix?

Hey, did that again. Anything else? Thanks!

[stale[bot]]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[benjamc]

Closed by #1097