Scala avoid using null

Question

I hava a project on github that is analysed by codacy . The analysis suggest to "Avoid using null" for the following line of code:

def doSomethingWithPath(path:Path) = {
    require(path != null, "Path should not be null") //<-to avoid
    ...
}

What is the simplest scala idiomatic thing to do to fix it?

Answer 1

I would keep it as is. You aren't really using null here, just guarding against it. The alternative could be to just delete that line altogether, and decide to not handle the null at all. Ignoring the possibility of null might be fine in a well built code base where it shouldn't come up anyway and null would be a bug, but a simple guard to catch it could prevent more subtle bugs from showing up in case something went wrong and null actually happens.

Answer 2

If path might actually be null this is probably the simplest.

require(Option(path).isDefined, "Must have a real Path")

Answer 3

the most idiomatic way would be to avoid the require (not sure but I have the idea it can thrown an exception - something Scala heavily recommends against)

def doSomethingWithPath(path:Path): Option[stuff] = { // will return an option of the type you were returning previously.
     Option(path).map { notNullPath =>
       ...
     }
}

Now the possible null case will be returned to the caller, that can/will propagate the returned Option until the layer that knows how to handle it properly.

Note: it is possible that the best place to handle the null case is inside you function. In that case you should do something like

Option(path).map { notNullPath =>
    ...
}.getOrElse(/* take care of null case */)

If you do want to keep the require, then the answer by jwvh would be my choice also

Answer 4

There's no need to explicitly check for null or wrap path in an Option. You can do this:

 path match {
  case p: String => Option(doSomethingWith(p))
  case _         => None //if path is null this will be returned
 }

That will return an Option, which may not be what you want, but in that case instead of producing a None, raise an exception. require will raise an exception in your example anyway so if that's what your caller expects just do it explicitly.