I'm not sure what others recommend. I know that it could be a security issue but in general you should not be getting any errors so display_error will never show anything. When it does, the screen capture that the user can send us will be much more valuable than a typical “it doesn't work” or “it gives me a blank screen”. I mean, errors MUST be fixed, and we need information to fix them. So I think it is good. In any case, you can set it as you want because this does not affect the functionality of the application.

This is no problem, I updated that file to be in sync with the installation, since you did the installation before my change your file is correctly defined and the incoming change is trying to apply the same structure, so just undo your changes and execute the pull:

git checkout modules/ProjectMilestone/schema.xml
git pull

Have a read at this user's experience