Scala function – Type mismatch. Required: Null. Found: String

I have a problem with type mismatch in Scala Function. Compiler returns an error:

  def isLarger(inputNum: Int) = {
      var res = null
      if (inputNum.>(10)) {
          res = "aaa"
        }
      res
      }

If inputNum larger than 10, return String "aaa" if not, return null.
But Type match.
Why? Any idea what could be the problem?

>Solution :

Try to add type declaration

var res: String = null

By the way, you don’t need a var. If-else is an expression

def isLarger(inputNum: Int) = {
  val res: String = 
    if (inputNum > 10)
      "aaa"
    else null
  res
}

The concept of absent value is better expressed with Option rather than null

def isLarger(inputNum: Int) =
  if (inputNum > 10)
    Some("aaa")
  else None