Ember

Describe the bug
When running yarn build and pressing enter, it states the following error:

It would be nice if the tool did not allow empty selections.

To Reproduce

• Run yarn build
• Press enter

System
Please paste the results of npx sb@next info here

Issue Summary

I have Ghost Self-hosted.

When I try to import my subscribers from Substack, it shows this error as shown in the image.

I tried searching everywhere but no solution. I also tried to manually create the Members folder on the server but still no luck.
![CleanShot 2021-08-07 at 20 42 50@2x](https://user-images.githubusercontent.com/5517129/128604907-9d7cab8d-0d6b-4cbb

By default ember-cli updates a number of the "app trees" to be from tests/dummy when developing an addon locally. We do this for app, styles, templates, public, and tests trees (handled inside lib/broccoli/ember-addon.js).

Unfortunately, we do not forward the apps vendor tree to tests/dummy/. This means that our addon's treeForVendor is called, but then subsequently clobbered by the "apps

Is your feature request related to a problem? Please describe.
I understand Ember Inspector is for the development and Debugging phase. And I am of the opinion that, having access to the private (by convention, underscore prefixed) fields/property is a very useful feature when hunting for problems like why a certain computed property based on other field and property have an unexpected value.

Documentation discusses Bootstrap 3 at some places. As we drop support for Bootstrap 3 in v5, that documentation should be removed or reworded. Searching for BS3 should be a good starting point.

In case you came along arguments or argument values only supported for BS3, please open an issue to remove them. Or even better: Create a dedicated pull request removing that argument.