CatStation/Content.Shared/Gravity/SharedGravitySystem.cs

namespace Content.Shared.Gravity
{
    public abstract class SharedGravitySystem : EntitySystem
    {
        public override void Initialize()
        {
            base.Initialize();
            SubscribeLocalEvent<GridInitializeEvent>(HandleGridInitialize);
        }

        private void HandleGridInitialize(GridInitializeEvent ev)
        {
            EntityManager.EnsureComponent<GravityComponent>(ev.EntityUid);
        }
    }
}