So first of all, head as it is in Prelude is a partial function. The error isn't a null pointer exception, it is an issue with head not being defined on empty

So first of all, head as it is in Prelude is a partial function. The error isn't a null pointer exception, it is an issue with head not being defined on empty lists. I personally would never use head in code I write. Instead I'd use a version which looks like [a] -> Maybe a which does properly solve the null problem. On top of that, the compiler can warn/error if partial functions are used. I do this for all of my projects. There has been a lot of debate over these functions should even existing in Prelude. I think they are a blight on the language.