Expose RID.is_null() to scripting

[aaronfranke]

I was working on some C++ code and trying to make it compatible with both in-engine module code and GDExtension C++ godot-cpp, and I found that the code uses .is_null() on an RID, which works in-engine (used 390 times), but not in GDExtension because the API is not exposed. This PR exposes it. Regardless of this PR, a workaround that is compatible with the currently released godot-cpp API is to use ! with .is_valid() on an RID instead of .is_null().

[Ivorforce]

I'm not sure we need both.
I've already been apprehensive of there being two methods doing the same (give or take a ! anyway) inside the engine, but exposing the second function sets their difference in stone.

I suppose it comes down to if we ever expect there to emerge an actual implementation difference in the future. If not, we shouldn't expose both, and in my opinion, even consider removing one of the two functions altogether.

[aaronfranke]

@Ivorforce I'm fine with not having both if that's the consensus, but only if the internal one is removed too. The internal and external APIs should match for trivial things like this.

[AThousandShips]

I'm in favor of binding this, it's far clearer and the exposed API should match IMO

[Mickeon]

If C++ normally supported not there would be no discussion, but alas. Doc is fine

[akien-mga]

Makes sense for the sake of GDExtension and C++ modules compatibility.

[Ivorforce]

As I said above, I'm not at all convinced we should expose the same functionality twice.
If it's alright with everyone, I'd like to discuss this at the core meeting next Wednesday.

[clayjohn]

As I said above, I'm not at all convinced we should expose the same functionality twice. If it's alright with everyone, I'd like to discuss this at the core meeting next Wednesday.

Yes, let's discuss. We definitely shouldn't be exposing an API "for consistency" with an internal API when we don't even have consensus on the internal API

[beicause]

In C# Rid is a separate wrapper and IsValid is a property.

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

Line 46 in 5dd7696

public bool IsValid => _id != 0;

I agree is_null is just a internal code style of Godot and it is not necessary, and Rid.IsNull might confuse me because there's also nullable Rid (Rid?) in C#. For example: if( rid != null ) if( rid.IsNull ) {} isn't clearer than !rid.IsValid.

[aaronfranke]

If one is kept, I agree that is_valid is the better one to keep, but then we need to remove is_null internally.

[aaronfranke]

Note that !is_valid was recently replaced with is_null in #100776 and #96076 in late 2024.

[AThousandShips]

For Ref yes, this is RID which was not changed