THREESCALE-8979: Fix the issue with not being able to remove default plan

[mayorova]

What this PR does / why we need it:

Fix the issue with not being able to remove default plan.

Which issue(s) this PR fixes

Fixes https://issues.redhat.com/browse/THREESCALE-8979

Verification steps

1. Create a product, and an application plan for it
2. Open the application plans list and see that No plan selected is shown for the Default plan
3. in the drop-down select an application plan and click Change plan. The plan is changed and the "success" flash message is shown.
4. Select No plan selected again, and click Change plan.
5. The default plan is unset, the page is reloaded and the "success" flash message is shown.

Special notes for your reviewer:

In Flow there was an ignore message explaining why there was an empty string: https://github.com/3scale/porta/pull/2974/files#diff-5360738f38dabacb7a4d30fca57a8de39dd864cae351edae17bfe5c0b70fdae1R27

The ID of the default plan was changed from '' to -1 in the Typescript PR: https://github.com/3scale/porta/pull/3054/files

[josemigallas]

The whole id: number | string was a big mess (I guess it's still is) so let's better leave that alone. This should be handled by the Select, outside of it we don't care what the server needs. There is a leftover TODO from then migration to TS:

porta/app/javascript/src/Common/components/Select.tsx

Line 80 in c6070f9

{/* TODO: should it be `value={item.id > -1 ? item.id : ''}`? */}

At the time I didn't remember why it was '' vs. -1 so I never answered the question.

Anyway, I think the biggest problem is there was no 🥒 test for this. That should come first.

[mayorova]

let's better leave that alone
What do you mean @josemigallas ?

Do you mean that this fix is not valid, and should be done in a different way? (in the Select component)

[josemigallas]

let's better leave that alone
What do you mean @josemigallas ?

Do you mean that this fix is not valid, and should be done in a different way? (in the Select component)

Yes

[josemigallas]

Suggested change

	{/* Controllers expect and empty string for some operations (such as unsetting the default plan) */}
	{/* Controllers expect an empty string for some operations (such as unsetting the default plan) */}

[josemigallas]

🥒