Change misleading comment in 'Your first 3D game'

[fmnjose]

On the collision processing code (Chapter 6 - Jumping and squashing monsters) there is a misleading comment saying that the collision.get_collider() == null has the purpose of checking for a collision with the ground, while the purpose is to prevent a null pointer that happens when there are multiple collisions with a mob in a single frame.

This addresses the following open issue: #9355

• Bugsquad edit, closes: Please remove this code block, or add some explanation to it #9355

[Bamarin]

Not against this change, but rather curious: how can the collider be null?

You mentioned this happens after we squash the mob and delete the object (for subsequent collisions with the same mob, the collider will be null).
But we are breaking out of the look right after the squash, so that null check shouldn't be necessary.

Indeed, it's missing in the C# counterpart.
Is it because the break statement acts differently in GDscript?

[raulsntos]

Indeed, it's missing in the C# counterpart.
Is it because the break statement acts differently in GDscript?

No, the check also exists in C#:

if (collision.GetCollider() is Mob mob)

This checks that the collider instance is of type Mob and that it's not null.

[fmnjose]

Not against this change, but rather curious: how can the collider be null?

You mentioned this happens after we squash the mob and delete the object (for subsequent collisions with the same mob, the collider will be null). But we are breaking out of the look right after the squash, so that null check shouldn't be necessary.

Indeed, it's missing in the C# counterpart. Is it because the break statement acts differently in GDscript?

I've tried removing the code block, and I started getting null pointers when hitting the mobs from certain angles.
I printed the collision counters and noticed that in those cases there were multiple collisions with the mob, and the first collision processed would delete the object, inducing a null pointer for the next ones being processed.

Either way the block of code does not serve the purpose of checking for a collision with the ground, as it will never have a null collider, and removing this code doesn't affect the collision with the ground.