That's actually pretty normal. Don't worry. It will fix itself next time. It isn't really the entire scale missing. More like a layer of the scale. It usually only happens around the head. There is nothing you can do and it won't harm the snake at all. Just bump humidity the next time it goes into a shed cycle.
*edit.. Also, I've seen this happen more often to pastels than any other morph. I don't know why, but it does happen. Sometimes even if the humidity is high.