If all layer candidates were bad then the layer count would not match the collect count and this would cause an error. Now if there were no layers or we removed all the layer_ies candidates we restore the None layer so that we don't trigger the error condition.
If all layer candidates were bad then the layer count would not match the collect count and this would cause an error. Now if there were no layers or we removed all the layer_ies candidates we restore the None layer so that we don't trigger the error condition.
closes https://github.com/open-physiology/apinatomy-models/issues/28