Wrong compilation with nullability support

[trejjam]

Hi, I have noticed that the target framework changed with the new version. That breaks the nullability annotations.

The issue is that the used preprocessor directive is NET8_0. To prevent similar issues in the future, it should be at least NET8_0_OR_GREATER.

html-agility-pack/src/HtmlAgilityPack.Shared/HtmlNode.Xpath.cs

Line 41 in 8490ad1

#if NET8_0

And since nullable annotations have been available since c# 8, which came with Net Core 3 it might be a good idea to use NET5_0_OR_GREATER. In case someone will lower the target framework again. https://learn.microsoft.com/en-us/dotnet/standard/frameworks#preprocessor-symbols

I can make the PR that will fix the issue, if you like.

[SerhiyBalan]

• 1.12.0 was a failure for those who use nullability in their projects.
• 1.12.1 was a particular win, as it fixed most of the issues.
• 1.12.2 feels like a step backward again.

[StefH]

This PR should fix it.

#598

[JonSaffron]

1.12.1 was a particular win, as it fixed most of the issues

One I bumped into a lot was with the HtmlAttributeCollection:

public HtmlAttribute this[string name]

As the getter returns null if the named attribute does not exist in the collection. Would love to see this updated.