Shouldn't maximebf/debugbar be patched instead? Can you please them a PR?

their code does check for NULL headers when printing so they are a possibility.

I read that in the issue on maximebf/debugbar, found the corresponding line in the code. This makes sense as a big fix now.

Can you please add a test case to back the behavior up?

I suggested an alternate fix in php-debugbar/php-debugbar#474

I fixed it for the time being now: php-debugbar/php-debugbar#475

I think we needed to reset it for a reason, which isn't currently possible. We're now overriding this method which solves it, but either a nullable check or a reset method would be helpful.

I think we needed to reset it for a reason, which isn't currently possible.

Do you want to contribute the reset method as a feature for 5.4?

Actually I prefer making the setter null able as a bugfix :)

Good catch, thanks @rrpadilla.