C#: Fix errors when creating Variant from null array

[zaevi]

Returns default Variant (nil) if the Span<*> is null.

This also adds the disposal of temporary array.

• Fix C# Array of StringNames Exported property with null default value causes null value exceptions in editor and in game. #89586

• Fix Exporting NodePath as a C# array don't work #82362

• Supersedes Fix C# array null handling #82388

[paulloz]

Good catch! I think this is fine, yep.

[raulsntos]

Thanks for the contribution, I'd like to understand the PR a bit better before approving.

Returns default Variant (nil) if the Span<*> is null.

I'm not sure what you mean by this, Spans can't be null because they are value types. Can you explain why this change is needed? Do empty arrays work before/after this PR?

The current issue is probably because of checks like:

godot/modules/mono/glue/GodotSharp/GodotSharp/Core/Array.cs

Lines 88 to 91 in fe01776

	public Array(Span<StringName> array)
	{
	if (array == null)
	throw new ArgumentNullException(nameof(array));

I imagine this was a copy-paste mistake. But then Array.Empty<StringName>() should throw as well.

[raulsntos]

This looks weird to me, Spans are value types so they can't be null. The only reason why they can be compared to null is because there is an implicit conversion from arrays to spans and the null literal can be converted to array so basically this is doing this:

if (from == (Span<StringName>)((StringName[])null))
    return default;

Which means this also returns a default Variant for empty arrays and I'm not sure we want that.

[zaevi]

It's ok because for empty arrays, the span won't be null (as its _pointer points to that array). So, it returns default Variant only when the array is null.

[raulsntos]

That's true, I was thinking whether we should allow creating Godot.Array from null but on second thought I think the changes in this PR are more correct.

[akien-mga]

Thanks!