feat(form): allow Answers with empty value

[open-dynaMIX]

This commit adds the possibility to save/query Answers with null
values.

It also adds a new lookup mode ISNULL to the HasAnswerFilter. If
this lookup mode is used, the provided value (if any) is ignored.

Since graphql-core doesn't support null literals yet, the way for setting
the value of an Answer to None is to omit the value field
altogether.

Closes #790 and #800

BREAKING CHANGE: Answers are now allowed to have null values.

[winged]

Awesome work!

[czosel]

Why is this a breaking change? Aren’t we just being more permissive?

[open-dynaMIX]

Why is this a breaking change? Aren’t we just being more permissive?

I'm not 100% sure about that.

You could've relied on the backend to prevent null values in Answers. This won't work anymore.

To be safe, I'd consider all changes on the optionality of existing fields as potentially breaking.

[czosel]

In general this sounds reasonable, in this specific case I'm not so sure, since most of the code that relies on this is in ember-caluma anyway. I wonder what @kaldras and @anehx say about it?

[open-dynaMIX]

We claim to be web framework agnostic. So I don't think ember-caluma should have anything to do with the decision if this is a breaking change.

Of course I'm aware of the fact that noone is using caluma without ember-caluma atm ;)

[winged]

In general this sounds reasonable, in this specific case I'm not so sure, since most of the code that relies on this is in ember-caluma anyway. I wonder what @kaldras and @anehx say about it?

It's also (and mainly) about the type system. The value types changed from String! to String (where the missing ! denotes nullability). This by itself implies a breaking change, as you need to change the types in the mutations/queries as well.