Sebastian De Deyne on his blog:

Dynamic languages allow us to pass anything as a parameter without requiring a specific type. In turn, this means we often need to handle some extra validation for the data that comes in to our objects. This is a lightweight post on handling your incoming values effectively by normalizing them as soon as possible. It's a simple guideline worth keeping in mind which will help you keep your code easier to reason about.

https://sebastiandedeyne.com/posts/2016/normalize-your-values-on-input