`Entity.Get` not working

[mlange-42]

Working on some comparative ECS benchmarks over at go-ecs-benchmarks, I was not able to test component random access. I.e. accessing components for a specific entity, without the use of systems or queries.

I get panic: reflect: call of reflect.Value.Type on zero Value.

Code to reproduce:

func runEnto(b *testing.B, n int) {
	b.StopTimer()
	world := ento.NewWorldBuilder().
		WithDenseComponents(comps.Position{}).
		Build(1024)

	entities := make([]*ento.Entity, 0, n)
	for i := 0; i < n; i++ {
		e := world.AddEntity(comps.Position{})
		entities = append(entities, e)
	}
	rand.Shuffle(n, util.Swap(entities))

	b.StartTimer()

	for i := 0; i < b.N; i++ {
		for _, e := range entities {
			var comp *comps.Position
			e.Get(comp) // <--- crashes here
			comp.X++
		}
	}
}

Stack trace:

reflect.Value.typeSlow({0x0?, 0x0?, 0xc0001812e8?})
        C:/Programs/Go/src/reflect/value.go:2687 +0x10e
reflect.Value.Type(...)
        C:/Programs/Go/src/reflect/value.go:2682
github.com/wfranczyk/ento.(*Entity).Get(0xc000022750, {0xc000069f10?, 0xc000069ec8?, 0x1?})
        C:/Users/mlange/go/pkg/mod/github.com/wfranczyk/ento@v0.1.0/entity.go:42 +0xf0
github.com/mlange-42/go-ecs-benchmarks/bench/random.runEnto(0xc0001b0008, 0x1)
        C:/Data/Hack/go/arche/go-ecs-benchmarks/bench/random/ento.go:30 +0x334
github.com/mlange-42/go-ecs-benchmarks/bench/util.RunBenchmarks.func1(0xc0001b0008?)
        C:/Data/Hack/go/arche/go-ecs-benchmarks/bench/util/util.go:37 +0x22
testing.(*B).runN(0xc0001b0008, 0x1)
        C:/Programs/Go/src/testing/benchmark.go:193 +0xf0
testing.(*B).run1.func1()
        C:/Programs/Go/src/testing/benchmark.go:215 +0x48
created by testing.(*B).run1 in goroutine 1
        C:/Programs/Go/src/testing/benchmark.go:208 +0x90