If you are printing small parts and you keep noticing holes in very small detail, the setting you want to change is the Minimum Infill Length. Default is 5mm, meaning no infill will be generated for anything less than 5mm. That's a lot for small models and will result in holes. It saves time when printing big models, but remember this setting when you are printing tiny parts.
I have mine set at the nozzle width of 0.4mm and just leave it there. It may add time, but I prefer the quality over the speed and the majority of my models are small parts.