And.eval short circuiting

[Zack Sampson]

It seems like And.eval can avoid calculating right.eval if left.eval returns 
null. Is there a reason it's written like it is?


override def eval(input: Row): Any = {
  val l = left.eval(input)
  if (l == false) {
    false
  } else {
    val r = right.eval(input)
    if (r == false) {
      false
    } else {
      if (l != null && r != null) {
        true
      } else {
        null
      }
    }
  }
}