HandleEvent.cs

public async Task Handle(PurchaseOrderLineChange poChangeEvent)
{
    var currentPol = await repository.GetBy(poChangeEvent.PurchaseOrderLineId);
    
    if (currentPol.Version <= poChangeEvent.Version)
    {    
        currentPol.ApplyChanges(poChangeEvent);
        await repository.Update(currentPol);
    }
}