Fixes: Consistency for Nullable reference types in LINQ extensions methods #12692

Prerequisites

• [x] I have added steps to test this contribution in the description below

If there's an existing issue for this PR then this fixes - https://github.com/umbraco/Umbraco-CMS/issues/12692

Description

Removes some of the pain around nullable reference types.

Makes querying Children() and similar axis methods simpler by ensuring they never return null - they will always return an empty collection.

Also ensure that the Root() method can never return null, as there always should be root content.

Finally, ensures the .Name property can never be null. It will default to string.Empty. Again, this makes referencing it simpler as avoids the need to add extra null checks.

All Unit tests pass.

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Sorry for the delay @DanDiplo - we rebased your changes and this all seems good to go for v11. Thanks again for the help! 👍

@nul800sebastiaan No worries, glad to help! Looking forward to v11

Hi,

looks like this makes a breaking change?

(specifically, https://github.com/umbraco/Umbraco-CMS/pull/12703/files#diff-04ea84454360ff165d2411fe7f2fb64ceb3f8f2ee5de57789a0f424d35608a5fL694-L699 )

For example on the Umbraco starter kit - if you add the following to the master.cshtml template:

@{
    var productsPage = Model.AncestorOrSelf("Products");
    if (productsPage != null) {
      <h2>[@productsPage.Name]</h2>
    } else { 
      <h3>No Product parent</h3>
      }
}

in v10 or below you would expect "No Product parent" on any page that isn't the poducts or a product page. so for example on the homepage it would say "No Product Page"

on v11.1 this returns "[Home]" when on the homepage. which means you can no longer use the logic above if you want to put something in a master or parent template that only renders in certain parts of your site tree.

@KevinJump I think you are right in regard to the AncestorOrSelf method. The idea was that all LINQ methods that returned collections should never return null - they should always return an empty collection - so you could chain methods without worry. But the AncestorOrSelf() method looks like it should return null if not found as it just returns a single node. Not sure why I changed that...

I think the other methods are OK, though? Is it just that one? I can do a PR to fix if it's just that...

I ran in to this issue when upgrading a v9 site to v11. @DanDiplo you are correct that it should return null. Can you make a pull request to fix it as you suggested?