[NFTs] Allow to set the role to None

[jsidorenko]

This PR allows setting the Issuer/Admin/Freezer accounts to None without the ability to change it back (except for root calls).
This is useful for cases when the collection is created, all the items are minted and now we want to be 100% sure no one will mint any more items, or change the metadata, or disable some item's transfer.

[gilescope]

Love PRs that minimise trust.

[jsidorenko]

bot rebase

[paritytech-processbot]

Rebased

[ruseinov]

Curious why there isn’t any change to the logic that checks those roles, since they’re optional now - that should have reflected on the check logic?
One other question - what happens if the admin unsets itself?

[ruseinov]

looks good, would still be nice to make sure the answers to my questions make it to github for posterity.

[jsidorenko]

Curious why there isn’t any change to the logic that checks those roles, since they’re optional now - that should have reflected on the check logic?

That's the beauty of that PR :) All the business logic is already in place and was mostly set here: #13482, so now if you remove the Admin role and the previous admin will try to call some admin-related method, the validation won't allow that.

[jsidorenko]

One other question - what happens if the admin unsets itself?

Only the collection's owner could unset the admin.

[jsidorenko]

bot merge